Early Instruments of Astronomical Spectroscopy. By Peter Abrahams. (This paper is a presentation, accompanied by a quantity of transparencies, which have not yet been scanned.) -------- The development of spectroscopy in astronomy is the history of astrophysics, as massive a history as any, and to trim it to more manageable size, presented here will be the highlights of 19th century spectroscopy, which consisted of exhaustive collecting, cataloging, and classifying of data. Theory mostly came later, with the notable exception of Norman Lockyer, and so the development of the understanding of spectra will not be considered. Instead, we will focus on the instruments that were attached to 19th century telescopes and the more interesting phenomena they revealed. Since we want to avoid any romanticized revisions of cold science, I opened with this fine image of Aristarkh Appolonovich Belopolsky hard at work at the 30 inch Clark refractor at Pulkova, gaining a stellar radial velocity and a backache to boot. As bad as that looks, some of Belopolsky's colleagues at Pulkovo starved to death in the early 1920s, and all but one (Nikolai Kozyrev) died in the gulags and terror of Stalin. A few highlights from earlier years: Isaac Newton explored the spectrum of sunlight in 1666. He also observed the spectrum of Venus, collecting the planetary light with a lens, placing a prism just before the focus, and seeing the image "drawn out into a long and splendid line", as described in a letter to Henry Oldenburg in 1672. Spectral lines were first observed by Thomas Melvill of Scotland, in 1752, who burned alchohol and introduced salt and other chemicals. Observing with a prism, he noted abrupt brightening of yellow and other colors in the continuous spectrum. David Rittenhouse of Pennsylvania built a diffraction grating of fine wire wrapped around a frame, observing six orders of spectra, measuring their angular displacement, and discussing the laws governing their displacement. Brooke Hindle describes Rittenhouse as the inventor of the diffraction grating. This was in response to being asked, why the view of a light through a fine handkerchief displayed a grid of lines that did not move when the cloth was moved. Rittenhouse described the effect as due to “the inflection of light in passing near the surfaces of bodies, as described by Newton.” In the late 1780s, he made a grating of hair with 106 lines per inch, then used thicker hairs to create slits that were about 1/250 inch wide. This allowed him to see 6 bright lines on each side of the cental line, and to see spectral colors in the outer 4 lines, which broadened until they almost touched in the outermost lines. He measured the angular displacement of these orders with a prism spectroscope and micrometer. He extrapolated from his measurements to conclude that the nth order had an angular displacement that was n times that of the first order. Hindle notes that his published results were discussed in England with the expected antagonistic nationalism, and his experiments were repeated by Henry Cavendish. The fact that red rays were more diffracted than blue, which was known to Newton, was sufficient to disprove the corpuscular theory of light and propound the wave theory. However, these important findings did not exert their due influence because they are a classic example of the result that fills no need and is premature in its application. William Herschel in 1800 used a prism & a thermometer to learn that the rays providing the maximum heating effect were beyond the visible red rays. (Herrman’s Herschel to Hertzsprung notes that he was investigating telescope design when this discovery was made.) J. W. Ritter of Germany, in 1801, found that rays beyond the violet caused the greatest blackening of silver chloride. Thus was the spectrum extended in both directions beyond visible light. Thomas Young used a diffraction grating, made of a glass plate with 500 grooves per inch, to measure the wavelengths of sunlight at different colors, establishing the nature of color in the wavelength of light. He experimented with the spacing of the grooves and the angle of diffraction, obtaining spectra in four orders, and publishing his results in 1802. William Wollaston in 1802 published a paper describing a solar spectrum and seven dark lines within it. The importance of these lines was not realized by Wollaston or his readers. He used a slit one twentieth of an inch wide, and viewed directly through a prism of flint glass held in front of his eye. Mary Somerville was shown this demonstration and presented by Wollaston with a prism made by Fraunhofer. As a sidelight, Wollaston inherited an interest in astronomy from his father Francis Wollaston, who had a private observatory with a Peter Dollond triplet telescope; and whose rare, privately printed autobiography 'The Secret History of a Private Man' explains that his pursuit of astronomy was intended to separate him at a "distance from the misrepresentations of narrow minded bigots". Truly a figure worth investigating. Joseph Fraunhofer has an eminent position in this history, and again his contribution was a result of his work in improving achromatic telescope objectives. The fine quality glass developed by the Swiss Pierre Guinand at the Benediktbeuern glassworks near Munich allowed the construction of prisms of superior quality. Joseph Fraunhofer assumed control of these works and researched the dispersion of this glass, by measuring the refractive index of monochromatic light of different wavelengths. Since color as perceived by the eye has no precisely deliminted number, he needed to find markers in the spectrum at various wavelengths. He noted the bright double line now known to be from sodium in various flame sources. "I wished to find out whether a similar bright line could be seen in the spectrum of sunlight as in the spectrum of lamplight, and I found,with the telescope, instead of this, an almost countless number of strong and feeble vertical lines...." Circa 1814, he used a slit in the shutters of his window, a 60 degree objective prism of flint glass, and a 25mm telescope to view the solar spectrum. He observed the multitude of lines, labelled the 10 brightest with letters, and measured precise positions for 350 lines, which have become known as the Fraunhofer lines in the solar spectrum. He studied them but did not explain their origin. Later work used a diffraction grating made of wire, of diameters between .04mm and .6mm. This was wrapped on a frame, spaced by .0528 mm to .6866 mm, (although there is no note in my sources that justifies this accuracy) and placed in front of the objective. 10 gratings were made, and the wavelength of the sodium D line was found to be .0005888 mm, a very accurate result, obtained not by directly measuring but by observing the several orders of spectra & interpreting them using the wave theory of light. By 1823, he had made two gratings on glass, with lines spaced by .0033 mm and .0160mm. Using the 25 mm telescope, Fraunhofer observed the spectra of Venus, noting it had the same nature as sunlight; of Sirius, noting three bands which did not appear in sunlight; and of other bright stars, noting variations in the lines. After 1820, he used a 10 cm telescope with a 37 degree objective prism, the earliest objective prism spectroscope, [Daumas: Rochon 1770s] to observe the spectra of the Moon, Venus, Mars, Capella, Castor, Pollux, Procyon, Sirius, and Betelgeuse, in which he saw countless lines, only some of which were found in sunlight. All this before his death from tuberculosis at age 39 His equipment was used circa 1838 by J. Lamont of Munich's Royal Observatory on their large refractor to observe spectra of fourth magnitude stars. In 1823, John Herschel described the use of spectral lines to detect small amounts of chemicals, but the bright lines of sodium were found in all laboratory spectra, due to impure samples, and this prevented the recognition that each element has a unique spectrum. John Herschel published in 1840 his work on photographing the solar spectrum, but no lines were seen in the photographs. W.H. Fox Talbot of photographic fame wrote in 1826 on the use of spectra for chemical analysis, but it was William Swan in Scotland who realized circa 1856 that samples of an unprecedented purity were needed for analysis, which was the step needed for spectral analysis to begin, and the Swan absorption bands of molecular carbon in cool stars are named after him. In 1842, Edmond Becquerel of Paris photographed the solar spectrum using a slit, a flint glass prism, and a lens to focus the image onto a Daguerrotype plate, revealing the Fraunhofer lines into the ultraviolet and even down to the red region. Becquerel continued the nomenclature of the lines, and 30 years later Norman Lockyer noted that no one had yet duplicated the photograph of the entire spectrum, with lines, from the red to the UV. J. W. Draper, 1843, drawing of solar spectrum, further into red, where three more absorption lines were named, and into UV. David Alter of Pittsburgh used spectroscopes of his own making to classify the spectra of sparks and of flame. He began this work circa 1845 and published in 1854 [American Journal of Science, ref. King] on the spectra of metals, describing lines due to impurities and noting that an alloy shows evidence of its fractions. In 1855, he published on the spectra of gases, speculating on the colors of the aurora and on whether the elements in meteors could be found by examining their spectra. George Stokes in Cambridge, England, used a quartz prism to disperse the solar spectrum into a fluorescent solution of quinine sulphate. This emitted a light in the ultra violet region of the spectrum, and the spectral lines could be seen in the liquid, lines that he sketched and named, publishing his results in 1852. These lines were measured by E. Esselbach in Germany. Stokes continued his work in 1862, this time on the ultra violet spectra of metals. He fabricated a prism of quartz, with the axis of the crystal at an equal angle to all three faces, and a lens of quartz with the axis perpendicular to the plane of the lens. These spectra were seen on a fluorescent screen. Leon Foucault made a pivotal observation in 1849. Burning a carbon arc, he noted the orange emission lines it produced at the location of the D lines in sunlight; and the orange absorption lines seen in the continuous spectrum of the glowing arc tips. Although he refrained from explaining what he had seen, Foucault had shown that a chemical can cause either absorption or emission lines at its designated place in the spectrum, depending on whether the light source is behind it and of a hotter temperature, or if the chemical is itself luminescent. Physicist Robert Bunsen and chemist Gustav Kirchhoff independently discovered Foucault's finding during their time together in Heidleberg, in a very modest lab in a house that was then 150 years old. The new Bunsen burner was an important aid to their work, for it provided a high temperature flame of low luminosity, allowing the spectra of vaporized chemicals to be prominent in the light. Their experiment viewed the spectrum of the sun and that of salt in a flame, and they were expecting the two sodium lines to add together and cause the dark lines in the solar spectrum to become brighter. Instead, the vapor of sodium in the flame absorbed the light of sodium from the sun, and the lines appeared darker. They considerably developed their findings to their 1861 claim that "in order to effect the chemical analysis of the solar atmosphere, all that we require is to discover those substances which, when brought into the flame, produce lines coinciding with the dark ones in the solar spectrum." Kirchhoff went on to compare the spark spectra of 30 elements with the solar spectrum, simultaneously viewing the two using a very fine 4 prism spectroscope by the professor of astronomy C.A. Steinheil. For example, 70 emission lines seen in iron vapor matched with 70 dark lines in the solar spectrum. They found in the sun, among other elements, sodium, iron, magnesium, copper, zinc, barium, and nickel. Bunsen & Kirchhoff published their results in 1860 and 1861, only one year before Angstrom published a similar study. The idea that the composition of a star could be learned by the study of its light became a topic of great public appeal, and was as great a popular sensation as any scientific discovery. Spectroscopy was a very attractive field of study to the amateur scientists of the 19th century, and no doubt many of the direct vision spectroscopes to be found at antique shows today were used to admire the natural world without necessarily dissecting it. In 1858, Donati's comet was observed from Paris by an Italian astronomer named I. Porro, using a 60 mm refractor with a flint glass objective prism. The low intensity of light from the comet meant that Porro could not use a narrow slit and therefore could not see the Fraunhofer lines in the spectrum. Donati later observed three emission bands in comet 1864 I. G. B. Donati in Florence studied the spectra of stars after 1860, using a 41cm (16") chromatic lens, and a single prism spectroscope with a cylindrical lens to widen the spectrum. Note the swiveling viewing telescope, used to measure the lines in about 15 stars, with less accuracy than some of his contemporaries, in results published in 1863. Lewis Rutherfurd of NY, used his 11 inch Fitz, to study & classify stars into 3 groups, and improved his spectroscope by enabling the viewing of a comparison spectrum. He also experimented with carbon disulphide prisms. He wrote an 1863 paper that describes spectroscopes of Airy, Donati, & Secchi. Circa 1850, Rutherfurd was involved in the manufacture of reflection gratings, that were diamond ruled on speculum metal, used in labs & for solar studies. [published first Dec. 1862 Silliman's American Journal] Also in 1863 was published the work of George Airy, Astronomer Royal, Greenwich Observatory, using a single prism without slit or collimator to record the spectra of 19 stars in simple drawings wihout recording line positions. Angelo Secchi worked at the Collegio Romano Observatory in Rome, and had use of their 9.5 inch (24 cm) refractor. He used a direct vision spectroscope by J.G. Hoffman of Paris, after Jules Janssen had described & brought his pocket Hoffman spectroscope to Rome, worked very well on telescope, and Secchi ordered one for himself, which was the first of many such instruments used by Secchi Dec. 1862, began studies of planets & stars, 1863 published results, with classification of stars into two groups. In the next four years, he observed the spectra of about 500 stars and classified 400 into 3 groups. 1869, objective prism 15 cm dia., 12 degrees, on Merz . 33 papers on spectroscopy were published by Secchi before his death at age 59 in 1878. In 1877, he published a spectral catalog of 209 stars, and included a note on the possibility of measuring radial velocity using the displacement of lines, which was attempted by Huggins in 1878. Secchi observed & classified over 4000 stars, to the eighth magnitude, dividing them into 5 classes by temperature; discovering carbon stars, finding broadened hydrogen lines in Sirius & deducing that they were wider due to pressure. Nebulae were studied, some were found to be luminous gas. Studies of the planets included observing Jupiter, Saturn, Uranus, and Neptune, noting absorption bands in the continuous spectra of all four planets, and correctly deducing the presence of an atmosphere of different composition than the air of the earth. A comet seen in 1862 was seen to have a continuous spectrum with lines that indicated carbon in the comet. Meteors were viewed with a spectroscope & found to contain iron, magnesium, and sodium, which further established their correspondence with meteorites. Secchi made many contributions to solar spectroscopy. Sunspot absorption lines were seen to be variations of the normal solar lines. The presence of a solar atmosphere was deduced from the inversion of lines that he could observe with solar equipment made for him by Hoffman, Merz, and Amici. He measured the Doppler shift seen in prominences & deduced their velocity and their spiraling movements. William Huggins was an amateur with no training in science at the university level. He began observing spectra in 1862 and continued into the twentieth century. Used an 8 inch Alvan Clark objective in a Cooke tube & mount. Along with chemistry professor William Miller, he built a two prism spectroscope with a collimator, and a viewing telescope with a micrometer to accurately measure line positions. Huggins and Miller measured 70 lines in the spectra of Aldeberan, identifying 9 elements, four incorrectly; 80 lines in Betelgeuse. Huggins (and David Brewster) wrote that stars were red because their absorption lines were mostly in the blue, a mistaken idea because temperature is the primary determinant of color, but in fact a lesser cause of stellar color. In 1863 they published the first studies of stellar spectra, including comparison spectra of 24 terrestrial elements. Even at this preliminary stage, they concluded that bright stars resembled the sun and emitted light from a lower, hotter mass that was surrounded by a cooler atmosphere. In 1863, Huggins & Miller photographed the spectra of Sirius and Capella on wet collodion plates, producing a continuum but no lines. In 1864, Huggins & Miller began a study of the spectra of nebulae, disproving the contemporary idea that they all were unresolved stars when he found the emission lines in 8 objects, and explaining that they must be clouds of gas. In the next four years, studied 70 nebulae, one third of which had emission spectra, two thirds were stellar. The two were able to observe a nova in 1866, when a second magnitude nova in Corona Borealis showed absorption and emission lines and became the first nova to be so studied. Huggins observed Brorsen's comet and Winnecke's comet in 1868, with three emission bands in the coma that he matched with burning hydrocarbons in the lab, which sounds sophisticated but just refers to a candle flame. He was the first to photograph a cometary spectrum, Comet 1881b, showing bands in the UV that he concluded were from cyanogen. Huggins attempted to measure stellar radial velocities, and in 1868 published a study of Sirius, comparing the hydrogen beta line with that from a discharge tube placed ahead of the objective. The emission line from the tube was slightly offset from the absorption line of the star, by 1.09 Angstroms, and after correcting for the earth's rotation around the sun, he concluded that Sirius was receding by 29 miles per second, although an accurate value is 5 miles per second. In 1871, Huggins was loaned a 15 inch Grubb refractor and an 18 inch reflector by the Royal Society. With the Grubb, he measured radial velocities for 30 stars, with about the same accuracy. Huggins was interested in the spectrum beyond visible light, and learned that calcite is superior to quartz because it is more dispersive, and therefore the number of prisms could be kept to a minimum, which greatly assisted in obtaining the spectra of faint starlight. He experimented with a single prism of calcite or Iceland spar, cut so that the axis of the crystal was perpendicular to the flat side of the prism. Because of the birefringent nature of calcite, each position of the prism gave a single angle of dispersion for only one wavelength, and two angles for all other wavelengths. You’d think that might complicate measurements, but apparently the difference was too small to be significant in the range of wavelengths studied. [McGucken] William Huggins 1876, Adam Hilger sg, quartz lenses & calcite prism, 18 inch reflector at prime focus, guided using the reflection of the star off the polished slit jaws, viewed through a small viewing telescope. After the photographic work of Draper was published, he renewed his photography of stellar spectra, using dry plates, and trailed the star along the slit to widen the spectrum instead of a cylindrical lens. 1880, Browning, two prisms, 18 inch at Cassegrain focus. Published results 1880, raises issue of whether different spectra represent an evolutionary sequence, from Vega & other white stars to Betelgeuse & red stars. In 1882, he published on his spectrographic studies of comets and nebulae, noticing the 'forbidden' lines in the Orion nebula. 1896, new UV sg, 2 calcite prisms, quartz lenses, used in his Atlas of Representative Stellar Spectra, 1899. Huggins made only a few studies of the solar spectrum. He attempted to photograph the corona with a spectrograph but was not successful. When he heard of the techniques of Norman Lockyer for obtaining the spectrum of solar prominences, he set up a similar apparatus and then widened the slit of his spectroscope, which gave him a view of the prominence itself, in the light of each of its elements. Anders Angstrom of Uppsala, in 1868 published drawing of solar spectra with about 1000 lines, systematic error of about 1 A corrected in 1880s by his collaborator R. Thalen. Angstrom also studied the spectra of the aurora borealis and of gases. Backtracking a little, he wrote in 1853 that hot gases absorb and emit light of one wavelength, anticipating Kirchhoff's proof of the idea. It is therefore for good reason that when we wish to refer to a unit of 10^-8 cm, we just call it an Angstrom. Cornu extended Angstroms work to the UV Johann Zoellner is known for his independent work in photometry and instrument design, and his astrophotometer was vastly superior to earlier models and allowed the foundation of modern photometry. He installed a private observatory in the tower of his father's cotton printing factory near Berlin. In 1869, he introduced his reversion spectroscope, which divides the light between two direct vision spectroscopes that disperse the light in opposite directions, displaying the two spectra side by side. The Doppler shifts of individual lines are therefore doubled. Zoellner designed and built this spectroscope specifically to detect these shifts. This reversion spectroscope was used in 1871 by his student Vogel, along with Lohse to measure the rotation of the sun, and confirm an earlier visual estimate by Secchi. This was the first demonstration that the Doppler shift applies to light, in addition to sound. Other sources say that the first certain demonstration of Doppler shifted light was by C.A. Young, in 1876, using a Rutherfurd diffraction grating. This motion could be checked by comparing with values obtained by the motion of sunspots. The reversion method was developed for photography by Edward Pickering in 1896. C. Doppler theorized that frequencies of light and sound will change with radial velocity back in 1842. He believed that stars reveal their radial velocities in their colors, and that an unmoving star was white. His ideas were quite controversial and contrary to already established facts, and were defended by him in a vigorous and disputative manner, which retarded their acceptance for some time. Henry Draper of N.Y in 1872 had a slitless spectrograph with a quartz prism mounted on his 28 inch reflector. By 1876, he was using a slit spectrograph on a portrait lens. In the last of his active years, he used a Browning two prism spectrograph. In 1872, Draper produced the first photgraph of a stellar spectra to reveal the absorption lines, using a 28 inch reflector and a quartz objective prism. He saw 11 dark lines in the spectrum of Vega, including 7 in the UV, which was the first observation of these UV Balmer lines of hydrogen. Draper continued with spectrum photography, and in 1877 published a claim that emission lines of oxygen had been found in the photosphere (layer with granules) of the sun, an erroneous finding that caused a vigorous controversy with Lockyer and others. A rotating star shows broadened spectral lines, since part of the star is moving towards us and part is moving away. William Abney was the first to theorize that the velocity of rotation could be measured by the broadening of the lines, in 1877. Abney was a scientific photographer whose theory was rejected by the establishment, most vociferously by Vogel, but 20 years later Vogel found just this effect in his studies and published a retraction. Hermann Vogel was a leader in this field. 1870, Vogel was appointed director of a private observatory in Bothkamp, with an 11 inch refractor that was the largest in Germany, where he began spectroscopic observations of comets, nebulae, planets, stars, & made a catalog of 2600 lines in the light of the sun. In 1874, Vogel moved to Potsdam, in the Berlin area, where the observatory was under construction , and which was completed in 1879. Using a refractor by Hugo Schroeder of Goettingen that had a 30 cm aperture, and a Zoellner spectroscope, he continued a project to classify all northern stars to magnitude 7.5. Using a grating ruled by Wanscheff in Berlin, he attempted stellar spectroscopy in 1881, which was probably the first attempt at obtaining the spectra of a star, but it was not successful. 1885, the star S Andromedae became the first supernova to be spectroscopically studied, and Vogel was 3 nights ahead of his rivals in that observation. He observed only a continuous spectrum, although Nicholas von Konkoly noted four emission lines. In 1888, he began photographing spectra, using this instrument by Toepfer, and developed the technique to provide unequalled precision of measurement, with a goal of superior radial velocity results. His photographs revealed the effect of the earth's orbit on stellar velocities, and a paper with J. Scheiner in 1888 published spectral lines and Doppler shifts for Arcturus, Procyon, Rigel, and Sirius, results which gained him great acclaim. In 1889, Vogel used spectrophotography to reveal the first two spectroscopic binaries, Algol and Spica. Vogol and Scheiner used their data to learn the orbital velocity, dimensions of the orbit, and the total mass of the system. Algol had been a mysteriously changing star for 200 years, now shown to be an eclipsing variable. The Potsdam observatory was a leader in spectrum photometry. This instrument is attributed to Vogel, and was used to measure the intensity of light at various wavelengths. The results were corrected for atmospheric extinction, selective absorption by the glass of the telescope, and chromatic aberration of the optics. The results could be elaborated into an early estimation of the temperatures of stars. Vogel was a leading instrument engineer, working with manufacturers to improve his tools, as with this Hilger spectroscope. Lets return to Aristarkh Appolonovich Belopolsky , whose career highlights are worth remembering. Circa 1895, using a spectrograph on the 30 inch refractor, he confirmed that Saturn’s rings are in fact an orbiting mass of small satellites, and found that the spectrum contained an abundance of UV. Belopolsky used the spectroscope to verify that the rotation of Jupiter was faster at the equator, (9 hours and 50 minutes) than at higher latitudes (9 hours and 55 minutes),and confimed the result by studying 200 years of drawings of Jupiter. He studied the spectrum of Nova Aurigae of 1892 and found the rate of expansion of the remnant, along with a half dozen other novae. Belopolsky discovered & measured many spectroscopic binaries, was a pioneer of radial velocity studies, and studied the solar faculae and prominences. He built many of his spectroscopes and was noted for his elegant laboratory apparatus, which included a verification of Doppler effect in light, using a pair of oppositely rotating wheels that were like turbine blades made of mirrors. And he was an editor of the Astrophysical Journal on top of all that. The contributions of Alvan Clark & Sons. By 1862, a multi-prism spectroscope of Clark manufacture was in use at Yale. This instrument had an unusual design by Josiah Cooke, a Harvard professor of chemistry and mineralogy, who was also using a Clark spectroscope in his lab at that time. These four inch prisms were made of glass sections cemented with Canada balsam, in response to the difficulty of obtaining large glass of adequate quality. Other unusual prisms made by Clark include liquid carbon bisulphide in plate glass. Small sheets of glass were cemented with a glue and honey mixture, and a separate piece of glass which had been figured to an accurate flat surface was attached to the outside with castor oil. The largest such prisms were about 5 inches by 3 inches. In 1863, the Clarks made a spectroscope with nine carbon bisulphide prisms, with a new prism adjustment, also designed by Josiah Cooke and made for him, that had a central iron cone that was raised and lowered to spread or approximate the prisms. Since the index of refraction of carbon bisulphide changes radically with temperature, temperature of the set up needed to be kept constant. In spite of the difficulties in manufacture and use, the elaborate set up was useful because of the very high dispersion of carbon bisulphide. Charles A. Young at Dartmouth was one of the earliest astrophysicists, who in 1866 bought a 5 prism spectroscope costing $350 from the Clarks. It was designed so that spark spectrum could be placed in the field of view for comparison purposes, and an eyepiece micrometer was used to measure position of lines. While using this instrument during the total solar eclipse of 1869, Young discovered a means for pinpointing the moment of contact between the earth and moon. This Clark spectroscope was modified over the years but was used until 1963. Young designed a new spectroscope with 6, 60 degree prisms and one half prism of 30 degrees with a silvered back surface that sent the light back through the 6.5 prisms, giving the dispersive power of a 13 prism train. It was built by George Clark, who also contributed a design for prism adjustment. During the 1870 solar eclipse in Spain, Young discovered the reversing layer of the solar atmosphere with this instrument. A 6 prism model for Columbia in N.Y. used this reflection system to emulate a 12 prism spectroscope. MIT had a 6.5 prism Clark spectroscope of the same design, but theirs is noted as using the same telescope for collimator and viewing telescope, a detail that is either different or just omitted from the description of the others. Harvard bought a similar spectroscope in 1869, a 5 prisms of dense Munich glass that emulated 10 prisms by reflection. This one was taken to Kentucky for the 1869 eclipse. Edward Pickering of Harvard is a spectroscopist of such accomplishment that his work couldn’t possibly fit into a half hour talk and will be retained for a presentation on the more advanced instruments of astrophysics. However, he was a regular customer of the Clarks and used them to design and manufacture much of the equipment he used. The Draper stellar classification system was adopted in 1913 and based on results obtained with instruments that were mainly of Clark manufacture. The Clarks also made four objective prisms of 11 inch aperture for Harvard, to use on Henry Draper’s 11 inch photographic telescope. All four prisms could be mounted together to produce images of spectra that were over four inches long. This telescope was loaned to a university in Canton, China in 1947. Other spectroscopes were made in this era for Henry Draper, Amherst College, a single prism model for J.M. Van Vleck at Weslyan, a simple laboratory spectroscope for Rennselaer, a two prism model for the USNO 26 inch, and a spectroscope that could use either a grating or a prism for the very unusual 9.5 inch Clark at Princeton (with an objective whose elements can be spaced at different distances to adjust color correction for visual, photographic, or spectroscopic work. [Gaussian curves]) In the twentieth century, Vesto Melvin Slipher made a very large numer of important contributions to astronomy through spectroscopy. He used the Brashear 3 prism spectroscope bought by Percival Lowell for $2000. in 1901 for his observatory near Flagstaff, for use on the 24 inch Clark refractor. This was an improved copy of the Mills spectrograph at Lick Observatory, also by Brashear. It was made with great physical rigidity, and fine temperature controls, necessary for the finest measurements of spectral phenomena. Slipher arrived at Lowell that same year, and was instructed by Lowell to install and maintain the instrument. Slipher was painstaking in his studies of and modifications to his equipment, using improved optics and faster lenses, extending his studies into the red and infrared with better films, using the best possible measuring tools and calibrating everything to the highest possible degree. Beginning in 1902, Slipher accurately measured the rotation of Venus, Mars, Jupiter, Saturn and Uranus; by aligning the slit paralel to the equator of the planet and measuring the slopes of the absorption lines. Spectral bands were found in the light of some outer planets, later shown by Slipher and others to be from ammonia and methane. The rotation of the Andromeda galaxy was measured in 1915, using the inclination of the spectral lines, and in 1913 he found that NGC 4594 was also rotating, though he did not release the result until he got another spectrograph a year later. Nebulae such as the Merope nebula in the Pleiades were shown to be shining by reflected starlight, interpreted to indicate that the nebula was in fact a dust cloud. He discovered interstellar sodium and found the first solid evidence of interstellar calcium, when in the spectrum of a binary system, the calcium line showed no oscillation. Slipher studied the radial velocities of globular clusters, the spectra of comets, and of aurorae and the night sky. However, his work in spectrophotography of galaxies, achieving enough dispersion and resolution to measure their radial velocity, is probably his most significant contribution. In 1913, he released his findings that the radial velocity of the Andromeda nebula was 300 kilometers per second, in Lowell Bulletin Number 58. This was based on four observations, and for Slipher one result meant an exposure of as long as 60 hours. He obtained 39 of the first 45 radial velocity measurements for spirals, and was among the first to interpret them to mean that these nebulae are distant galaxies, publicly stating it in April of 1917. Slipher was also director of Lowell Observatory after the death of the founder, and supervised the planet search that resulted in the discovery of Pluto. The Brashear spectrograph was restored by Paul Roques, who found evidence of Brashear's craftsmanship and Slipher's fine tuning, with scribed reference marks & alignment shims in the instrument, which is now on display. Finally, lest we wallow in the past and forget that the present is a part of history, and that the present is certainly the golden age of astronomy, here is a reminder that spectrographic instruments continue to expand our horizons, not only to the distant galaxies, but to the nearby objects that have escaped our attention in the past. Faint stars that shine mostly in the infrared are numerous neighbors of ours, and a population of stars that show iron hydride and chromium hydride, instead of the oxides of these metals, as well as lithium, sodium, potassium, and cesium, in their spectrum are distinct in their chemistry and have been classified the L stars, a new grouping and a fruitful field for future study. ----------------- home page: http://home.europa.com/~telscope/binotele.htm