Nebulae.

American Philosophical Society, 1917.

First edition, extremely rare separately-paginated offprint, and a remarkable association copy, signed by Edwin Hubble. In this profoundly significant paper, Slipher reports his finding that, of 25 spiral ‘nebulae’ examined, 21 are receding from us at high velocities, thus anticipating Hubble in his two most important discoveries: that the universe is expanding, and that the nebulae are separate galaxies outside our own, implying that the universe is vastly larger than our own Milky Way galaxy. Slipher’s “systematic observations of the extraordinary radial velocities of spiral galaxies provided the first evidence supporting the expanding-universe theory” (Britannica). “For the eminent cosmologist Fred Hoyle (1915-2001), Slipher’s pioneering observations of redshifts [i.e. velocities of recession] should have led to his being credited with the discovery of the expanding universe” (Kragh & Smith, p. 143). When in 1929 Hubble published the law now named after him stating that galaxies were receding from us at velocities proportional to their distance away, it was Slipher’s velocity measurements he was using, although he neglected to give Slipher any credit at the time. Slipher also notes in this paper that his measurements imply that we are not at rest with respect to the nebulae on average. He deduces a mean velocity of 700 km/s and makes a tremendous intellectual leap: “For us to have such motion and the stars not show it means that our whole stellar system moves and carries us with it. It has for a long time been suggested that the spiral nebulae are stellar systems seen at great distances … This theory, it seems to me, gains favor in the present observations” (p. 7). This was eight years before Hubble measured the distance of the Andromeda nebula and settled definitively the ‘island universe’ question of whether the nebulae were objects inside or outside the Milky Way. “Vesto Melvin Slipher, a pioneer in the field of astronomical spectroscopy during his long career at Lowell Observatory at Flagstaff, Arizona, probably made more fundamental discoveries than any other observational astronomer of the twentieth century” (Hoyt, p. 411). OCLC lists Observatoire de Paris only; no copies in auction records.

Provenance: Edwin Powell Hubble (1889-1953) (signature on last page of text).

In 1901, Slipher (1875-1969) took a position working at the new Lowell Observatory with Percival Lowell (1855-1916). Gradually, Slipher became highly skilled with the observatory’s spectrograph, learning to take spectra of planetary atmospheres. In 1909 Lowell asked Slipher to turn his attention to the long-standing problem of the spiral nebulae, which Lowell believed were solar systems in the process of formation within the Milky Way. “For three centuries astronomers had observed and speculated about these numerous, but faint, diffuse objects, yet almost nothing about them was then known. Some believed that they were vast aggregations of stars beyond the Milky Way, ‘island universes’ as suggested by philosopher Immanuel Kant in 1755. Others felt they might be embryonic planetary systems in early stages of evolution and thus analogs of the primordial solar system … [Lowell] thought that if such objects were indeed incipient solar systems, they might show spectrographic similarities to the solar system itself. Early in 1909 he asked Slipher to observe what were then only classified as ‘green’ and ‘white’ nebulae, the latter group containing the enigmatic spirals, and to compare the spectra of their ‘outer parts’ with his spectra of the giant outer planets” (Hoyt, p. 421). It took Slipher four years of difficult and demanding work before he obtained significant results: he detected a blue-shift in the wavelength of light from the Andromeda nebula due to the Doppler effect, indicating that the nebula was moving at high speed toward us. “On February 3, 1913 he wrote Lowell that the Great Nebula in Andromeda was approaching the earth at the then unheard-of speed of 300 km/sec, the value, incidentally, that is accepted today. “It looks as if you had made a great discovery,” Lowell replied. “Try some other spiral nebulae for confirmation.”

“Slipher now turned his attention to a spindle-shaped, edge-on spiral in Virgo, designated NGC4594, and by April his spectrograms showed that its spectral lines were shifted far toward the red, indicating that it was receding from the earth at about 1000 km/sec, an astounding velocity at that time. “This nebula is leaving the solar system [sic],” he pointed out to Lowell, “hence it seems safe to conclude that motion in the line of sight is the real cause of these great displacements in their nebular spectra” … Slipher continued these observations through the next year. In August 1914, at the American Astronomical Society’s seventeenth meeting at Evanston, Illinois, he could announce radial velocities for fifteen spirals. “In the great majority of cases,” he reported, “the nebula is receding; the largest velocities are all positive … The striking preponderance of the positive sign indicates a general fleeing from us or the Milky Way”” (Hoyt, pp. 424-5).

Always very cautious about the interpretation of his observations, Slipher was reluctant to challenge in print Lowell’s view of the nature of the spiral nebulae, and did not do so until 1917 [in the present paper], by which time he had measured the velocities of 10 more spirals. Other astronomers immediately realised the significance of Slipher’s data. “The brilliant Danish astronomer Ejnar Hertzsprung (1873-1967) sent to Slipher: “harty [sic] congratulations on your beautiful discovery of the great radial velocity of some spiral nebulae. It seems to me, that with this discovery the great question, if the spirals belong to the system of the Milky Way or not, is answered with great certainty to the end, that they do not.” To Hertzsprung and others, the speeds of the spirals seemed altogether too great for them to be gravitationally bound to the stellar system, and the use of the radial velocities of the spirals to reinforce the claims of the island universe theory soon became common practice” (Smith (1982), pp. 21-22). Ten years later, using the 100-inch Hooker telescope at Mount Wilson, Hubble began to use the method of Cepheid variables, introduced by the Harvard astronomer Henrietta Swan Leavitt (1868-1921) in 1912, to estimate the distances of the nebulae whose velocities had been measured by Slipher, which confirmed that Andromeda was indeed a separate island universe (this would not have been possible using the instruments available to Slipher). But many astronomers still credit Hubble with the first proof of the ‘island universe’ theory.

Slipher’s discovery that most of the spirals are receding at great velocities already suggests, at least with hindsight, an interpretation in terms of cosmic expansion. “From a modern perspective, it could seem surprising that the discovery of the expansion of the universe was not announced at this point” (Peacock, p. 1). In fact, in 1917 the Dutch theorist Willem de Sitter (1872-1934) published his cosmological model which predicted an expanding universe with a correlation between distance and velocity, but it seems that Slipher was unaware of this. By 1925 Slipher had measured the velocities of 45 nebulae, 41 of which were receding, and several astronomers looked for the correlation predicted by de Sitter, but without reliable distance measurements little progress was made.

In 1927 the Belgian priest/cosmologist Georges Lemâitre (1894-1966) showed that his modification of de Sitter’s model predicted a linear velocity-distance relation, and even linked this to Slipher’s velocity data and Hubble’s emerging distance measurements (although he did not cite Slipher directly). However, it is Hubble’s name that is now attached to the velocity-distance relation. “In 1929, Hubble provided distance estimates for a sample of no greater depth [than Slipher’s], using redshifts due almost entirely to Slipher. Hubble’s distances turned out to be flawed in two distinct ways: in addition to an incorrect absolute calibration, the largest distances were systematically under-estimated. Nevertheless, he claimed the detection of a linear distance-redshift relation … This is undeniably a great irony: by combining Slipher’s effectively perfect velocity data with distance estimates that are so badly flawed, Hubble nevertheless routinely receives sole credit for the discovery of the expanding universe (including the assertion that he measured the redshifts, which is frequently encountered in popular accounts – and too often even in those written by professional scientists)” (Peacock, p. 10). “It is one of the great ironies of science that Hubble’s measurements of distance were later substantially revised due to significant systematic errors, while Slipher’s redshift measurements have stood the test of time remarkably well” (O’Raifeartaigh, p. 8).

Hubble at last made amends in 1953. “As Hubble was preparing a talk he wrote Slipher asking for some slides of his first 1912 spectrum of the Andromeda nebula, and in this letter he at last gave the Lowell Observatory astronomer due credit for his initial breakthrough. ‘I regard such first steps as by far the most important of all,’ wrote Hubble. ‘Once the field is opened, others can follow.’ In the lecture itself, Hubble professed that his discovery ‘emerged from a combination of radial velocities measured by Slipher at Flagstaff with distances derived at Mount Wilson’” (Bartusiak, p. 35).

Why did Slipher not receive the credit he deserved at the time? “The most important factor in the naming of Hubble’s law is undoubtedly one of social context; Hubble was a famous astronomer working at the world’s foremost observatory, while Slipher was a lesser-known figure working at a smaller facility best known for controversial claims concerning the observation of canals on Mars” (ibid.). Hoyt (p. 412) also sees Slipher’s personality as a factor. “Slipher was a reserved, reticent, cautious man who shunned the public eye and rarely even attended astronomical meetings, often sending his papers for others to read. He consistently postponed publication of his discoveries until he had confirmed them to his own satisfaction, and some of his results were published by others to whom he communicated them in his correspondence. Such distinguished astronomers and astrophysicists as Sir Arthur Stanley Eddington, Knut Lundmark, Gustaf Strömberg, Harlow Shapley, and Hubble were among the beneficiaries of this largesse.” “Indeed, it is remarkable that Slipher never formally published the full set of his painstaking redshift measurements, but allowed them to be circulated by Eddington and Strömberg instead” (O’Raifeartaigh, p. 9).

“Born on an Indiana farm, Vesto Slipher studied at Indiana University (B.A., 1901; M.A., 1903; Ph.D., 1909). In 1901 he joined the staff of the Lowell Observatory at Flagstaff (though he returned to Indiana at times for graduate study), and he became its acting director in 1916 and director in 1926. There he organized and guided the search that resulted in the discovery of Pluto in 1930. Slipher’s extensive investigations led to the determination of the rotational periods of several planets. His discovery of dark absorption bands in the spectra of Jupiter, Saturn, and Neptune led to the identification of some of the chemical constituents of their atmospheres. He demonstrated that many diffuse nebulae (clouds of dust and gas) shine by the reflected light of nearby stars and discovered the bright radiations of the night sky and their changes in intensity. He also proved that sodium and calcium are scattered throughout interstellar space” (Britannica). When Slipher was awarded the Gold Medal of the Royal Astronomical Society in 1933, the citation read: “In a series of studies of the radial velocities of these island galaxies, he laid the foundations of the great structure of the expanding universe, to which others, both observers and theorists, have since contributed their share”.

Bartusiak, ‘The cosmologist left behind,’ Sky & Telescope 118 (2009), pp. 30-35 (“Edwin Hubble usually gets the credit, but Vesto Slipher was the first to see the signs that the universe is expanding”); W. G. Hoyt, ‘Vesto Melvin Slipher, November 11, 1875 – November 8, 1969,’ Biographical Memoirs of the National Academy of Sciences 52 (1980), 410-419; H. Kragh & R. W. Smith, ‘Who discovered the expanding universe?’ History of Science 41 (2003), 141-162; C. O’Raifeartaigh, ‘The contribution of VM Slipher to the discovery of the expanding universe,’ pp. 49-62 in Origins of the expanding universe: 1912-1932, Astronomical Society of the Pacific Conference Series, Vol. 471, 2013; J. A. Peacock, ‘Slipher, galaxies, and cosmological velocity fields,’ pp. 3-24 in ibid; R. W. Smith, ‘The Origins of the Velocity-Distance Relation,’ Journal for the History of Astronomy 10 (1979), 133-164; ibid., The Expanding Universe: Astronomy’s ‘Great Debate’, 1900-1931, 1982.



Offprint from: Proceedings of the American Philosophical Society, vol. LVI, no. 5, 1917. 8vo, pp. 7 (journal pagination 403-409). Original printed wrappers. A fine copy.

Item #4724

Price: $15,000.00

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