The number of American astronomers in this period was very small. The by-laws of the Astronomical and Astrophysical Society of America state that a quorum is constituted by twenty members. By the year 1900 only nine doctorates had been granted in astronomy in America. In that year there were four astronomical doctorates: two from Columbia University for G. N. Bauer and Carolyn Furness; one from the University of Chicago for Forest Ray Moulton; and one from Princeton University for Henry Norris Russell.
Some idea of what was considered important scientific work in this period can be garnered from the prizes that were awarded. E. E. Barnard received the Gold Medal of the Royal Astronomical Society in part for his discovery of the Jovian moon Jupiter 5 and for his astronomical photography with a portrait lens. His steamer, however, was caught in an Atlantic storm, and he did not arrive in time for the celebration ceremony. He is described as requiring several days to recover from the storm, whereupon the RAS hospitably gave a second dinner for him. Barnard’s lecture seems to have been spectacular and made full use of that recently improved audio-visual aid, the lantern slide projector.
In his discussion of his photograph of the region of the Milky Way near Theta Ophiuchus he concluded that “the entire groundwork of the Milky Way … has a substratum of nebulous matter.” (Meanwhile H. K. Palmer reported no nebulosity in photographs of the globular cluster M13.) Barnard, who was a superb visual observer, expressed considerable doubts about Percival Lowell’s view of an inhabited and canal-infested Mars. In his thanks to Barnard for his lecture, the president of the Royal Astronomical Society, Sir Robert Ball, voiced concern that henceforth he “should regard the canals in Mars with some suspicion, nay, even the seas [of Mars, the dark areas] had partly fallen under a ban. Perhaps the lecturer’s recent experiences on the Atlantic might explain something of this mistrust.” Lowell’s views were not then in favor in England, as another notice in Observatory indicated. In response to an inquiry on which books had most pleased and interested him in 1896, Professor Norman Lockyer replied, “Mars by Percival Lowell, Sentimental Tommy by J. M. Barrie. (No Time for Reading Seriously).”
Prizes in astronomy for 1898 awarded by the Académie Française included one to Seth Chandler for the discovery of the variation in latitude; one to Belopolsky, partly for studies of spectroscopic binary stars; and one to Schott for work on terrestrial magnetism. There was also a prize competition for the best treatise on “the theory of perturbations of Hyperion,” a moon of Saturn. We are informed that “the only essay presented was that by Dr. G. W. Hill of Washington to whom the prize was awarded.”
The Astronomical Society of the Pacific’s Bruce Medal was awarded in 1899 to Dr. Arthur Auwers of Berlin. The dedicatory address included the following remarks: “Today Auwers stands at the head of German astronomy. In him is seen the highest type of investigator in our time, one perhaps better developed in Germany than in any other country. The work of men of this type is marked by minute and careful research, untiring industry in the accumulation of facts, caution in propounding new theories or explanations, and, above all, the absence of effort to gain recognition by being the first to make a discovery.” In 1899 the Henry Draper Gold Medal of the National Academy of Sciences was presented for the first time in seven years. The recipient was Keeler. In 1898 Brooks, whose observatory was in Geneva, New York, announced the discovery of his twenty-first comet—which Brooks described as “achieving his majority.” Shortly thereafter he received the Lalande Prize of the Académie Française for his record in discovering comets.
In 1897, in connection with an exhibition in Brussels, the Belgian government offered prizes for the solutions of certain problems in astronomy. These problems included the numerical value ofred prizes for the solutions of certain problems in astronomy. These problems included the numerical value of the acceleration due to gravity on Earth, the secular acceleration of the Moon, the net motion of the solar system through space, the variation of latitude, the photography of planetary surfaces, and the nature of the canals of Mars. A final topic was the invention of a method to observe the solar corona in the absence of an eclipse. Monthly Notices (20:145) commented: “… if this pecuniary reward does induce anyone to solve this last problem or in fact any of the others, we think the money will be well spent.”
However, reading the scientific papers of this time, one gets the impression that the focus had shifted to other topics than those for which prizes were-being given. Sir William and Lady Huggins performed laboratory experiments which showed that at low pressures the emission spectrum of calcium exhibited only the so-called H and K lines. They concluded that the Sun was composed chiefly of hydrogen, helium, “coronium” and calcium. Huggins had earlier established a stellar spectral sequence, which he believed was evolutionary. The Darwinian influence in science was very strong in this period, and among American astronomers T. J. J. See’s work was notably dominated by a Darwinian perspective. It is interesting to compare Huggins’ spectral sequence with the present Morgan-Keenan spectral types:
HUGGINS’ STELLAR SPECTRAL SEQUENCE
Order of
Increasing Age Star (and modern spectral type in
parentheses)
Young Sirius (A1V)
…….…
Altair (A7 IV-V)
Rigel (B8Ia)
Deneb (A2Ia)
…….…
…….… Vega (A0V)
Capella (G8, G0)
Arcturus (K1 III)
Aldebaran (K5 III) Sun (G0)
Old Betelgeuse (M2 I)
Note: The modern stellar spectral sequence runs, from “early” to “late” spectral types, as O, B, A, F, G, K, M. Huggins was very nearly right.
We can see here the origin of the present terms “early” and “late” spectral type, which reflect the Darwinian spirit of late Victorian science. It is also clear that there is a reasonably continuous gradation of spectral types here, and the beginnings—through the later Hertzsprung-Russell diagram—of modern theories of stellar evolution.
There were major developments in physics during this period and readers of Ap. J. were alerted to them by the reprinting of summaries of important papers. Experiments were still being performed on the basic radiation laws. In some papers, the level of physical sophistication was not of the highest caliber, as, for example, in an article in PASP (11:18) where the linear momentum of Mars is calculated as the single product of the mass of the planet and the linear velocity of the surface. It concluded “the planet, exclusive of the cap, has a momentum of 183 and 3/8 septillion foot pounds.” Exponential notation for large numbers was evidently not in wide use.
In this time we have the publication of visual and photographic light curves, for example, of stars in M5; and experiments in filter photography of Orion by Keeler. An obviously exciting topic was time-variable astronomy, which must then have generated something of the excitement that pulsars, quasars and X-ray sources do today. There were many studies of variable velocities in the line of sight from which were derived the orbits of spectroscopic binaries, as well as periodic variations in the apparent velocity of Omicron Ceti from the Doppler displacement of H gamma and other spectral lines.
The first infrared measurements of stars were performed at the Yerkes Observatory by Ernest F. Nichols. The study concludes: “We do not receive from Arcturus more heat than would reach us from a candle at a distance of 5 or 6 miles.” No further calculations are given. The first experimental observations of the infrared opacity of carbon dioxide and water vapor were performed in this period by Rubens and Aschkinass, who essentially discovered the v2 fundamental of carbon dioxide at 15 microns and the pure rotation spectrum of water.
There is preliminary photographic spectroscopy of the Andromeda nebula by Julius Scheiner at Potsdam, Germany, who concludes correctly that “the previous suspicion that the spiral nebulae are star clusters is now raised to a certainty.” As an example of the level of personal vituperation tolerated at this time, the following i
s an extract from a paper by Scheiner in which W. W. Campbell is criticized: “In the November number of the Astrophysical Journal, Professor Campbell attacks, with much indignation, some remarks of mine criticizing his discoveries … Such sensitiveness is somewhat surprising on the part of one who is himself given to severely taking others to task. Further, an astronomer who frequently observes phenomena which others cannot see, and fails to see those which others can, must be prepared to have his opinions contested. If, as Professor Campbell complains, I have only supported my views by a single example, I was only withheld by courteous motives from adding another. Namely, the fact that Professor Campbell cannot perceive the lines of aqueous vapor in the spectrum of Mars which were seen by Huggins and Vogel in the first place, and, after Mr. Campbell had called their existence in question, were again seen and identified with certainty by Professor Wilsing and myself.” The amount of water vapor in the Martian atmosphere that is now known to exist would have been entirely indetectable by the spectroscopic methods then in use.
Spectroscopy was a dominant element in late-nineteenth-century science. Ap. J. was busily publishing Rowland’s solar spectrum, which ran to 20,000 wavelengths, each to seven significant figures. It published a major obituary of Bunsen. Occasionally the astronomers took note of the extraordinary nature of their discoveries: “It is simply amazing that the feeble twinkling light of a star can be made to produce such an autographic record of substance and condition of the inconceivably distant luminary.” A major topic of debate for the Astrophysical Journal was whether spectra should be shown with red to the left or to the right. Those who favored red to the left cited the analogy of the piano (where high frequencies are to the right), but Ap. J. opted gamely for red to the right. Some room for compromise was available on whether, in lists of wavelengths, red should be at the top or at the bottom. Feelings ran high, and Huggins wrote to say that “any change … would be little less than intolerable.” But the Ap. J. won anyway.
Another major discussion in this period was on the nature of sunspots. G. Johnstone Stoney proposed that they were caused by a layer of condensed clouds in the photosphere of the Sun. But Wilson and FitzGerald objected to this on the ground that no conceivable condensates could exist at these high temperatures, with the possible exception of carbon. They suggested instead and very vaguely that sunspots are due to “reflection by convection streams of gas.” Evershed had a more ingenious idea. He thought that sunspots were holes in the outer photosphere of the Sun, permitting us to see to much greater and hotter depths. But why are they dark? He proposed that all the radiation would be moved from the visible to the inaccessible ultraviolet. This, of course, was before the Planck distribution of radiation from a hot object was understood. It was not at this time thought impossible that the spectral distributions of black bodies of different temperatures should cross; and some experimental curves of this period indeed showed such crossing—due, as we now know, to emissivity and absorptivity differences.
Ramsay had recently discovered the element krypton, which was said to have, among fourteen detectable spectral lines, one at 5570 Å, coincident with “the principal line of the aurora.” E. B. Frost concluded: “Thus it seems that the true origin of that hitherto perplexing line has been discovered.” We now know it is due to oxygen.
There were a great many papers on instrumental design, one of the more interesting being by Hale. In January 1897 he suggested that both refracting and reflecting telescopes were needed, but noted that there was a clear movement toward reflectors, especially equatorial coude telescopes. In a historical memoir, Hale mentions that the 40-inch lens was available to the Yerkes Observatory only because a previous plan to build a large refractor near Pasadena, California, had fallen through. What, I wonder, would the history of astronomy have been like if the plan had succeeded? Curiously enough, Pasadena seems to have made an offer to the University of Chicago to have the Yerkes Observatory situated there. It would have been a long commute for 1897.
AT THE END of the nineteenth century, solar system studies displayed the same mixture of future promise and current confusion that the stellar work did. One of the most notable papers of the period, by Henry Norris Russell, is called “The Atmosphere of Venus.” It is a discussion of the extension of the cusps of the crescent Venus, based in part on the author’s observations with the 5-inch finder telescope of the “great equatorial” of the Halsted Observatory at Princeton. Perhaps the young Russell was not yet considered fully reliable operating larger telescopes at Princeton. The essence of the analysis is correct by present standards. Russell concluded that refraction of sunlight was not responsible for the extension of the cusps, and that the cause was to be found in the scattering of sunlight: “… the atmosphere of Venus, like our own, contains suspended particles of dust or fog of some sort, and … what we see is the upper part of this hazy atmosphere, illuminated by rays that have passed close to the planet’s surface.” He later says that the apparent surface may be a dense cloud layer. The height of the haze is calculated as about 1 kilometer above what we would now call the main cloud deck, a number that is just consistent with limb photography by the Mariner 10 spacecraft. Russell thought, from the work of others, that there was some spectroscopic evidence for water vapor and oxygen in a thin Venus atmosphere. But the essence of his argument has stood the test of time remarkably well.
William H. Pickering’s discovery of Phoebe, the outermost satellite of Saturn, was announced; and Andrew E. Douglass of the Lowell Observatory published observations that led him to conclude that Jupiter 3 rotates about one hour slower than its period of revolution, a conclusion incorrect by one hour.
Others who estimated periods of rotation were not quite so successful. For example, there was a Leo Brenner who observed from the Manora Observatory in a place called Lussinpiccolo. Brenner severely criticized Percival Lowell’s estimate of the rotation period of Venus. Brenner himself compared two drawings of Venus in white light made by two different people four years apart—from which he deduced a rotation period of 23 hours, 57 minutes and 36.37728 seconds, which he said agreed well with the mean of his own “most reliable” drawings. Considering this, Brenner found it incomprehensible that there could still be partisans of a 224.7-day rotation period and concluded that “an inexperienced observer, an unsuitable telescope, an unhappily chosen eyepiece, a very small diameter of the planet, observed with an insufficient power, and a low declination, all together explained Mr. Lowell’s peculiar drawings.” The truth, of course, lies not between the extremes of Lowell and Brenner, but rather at the other end of the scale, with a minus sign, a retrograde period of 243 days.
In another communication Herr Brenner begins: “Gentlemen: I have the honor to inform you that Mrs. Manora has discovered a new division in the Saturnian ring system”—from which we discover that there is a Mrs. Manora at the Manora Observatory in Lussinpiccolo and that she performs observations along with Herr Brenner. Then follows a description of how the Encke, Cassini, Antoniadi, Strove and Manora divisions are all to be kept straight. Only the first two have stood the test of time. Herr Brenner seems to have faded into the mists of the nineteenth century.
AT THE SECOND CONFERENCE of Astronomers and Astrophysicists at Cambridge, there was a paper on the “suggestion” that asteroid rotation, if any, might be deduced from a light curve. But no variation of the brightness with time was found, and Henry Parkhurst concluded: “I think it is safe to dismiss the theory.” It is now a cornerstone of asteroid studies.
In a discussion of the thermal properties of the Moon, made independently of the one-dimensional equation of heat conduction but based on laboratory emissivity measurements, Frank Very concluded that a typical lunar daytime temperature is about 100°C—exactly the right answer. His conclusion is worth quoting: “Only the most terrible of Earth’s deserts where the burning sands blister the skin, and the men, beasts, and birds drop dead, can approach noontide on the cloudless surface of our satellite. Only the extrem
e polar latitudes of the Moon can have an endurable temperature by day, to say nothing of the night, when we should have to become troglodytes to preserve ourselves from such intense cold.” The expository styles were often fine.
Earlier in the decade, Maurice Loewy and Pierre Puiseux at the Paris Observatory had published an atlas of lunar photographs, the theoretical consequences of which were discussed in Ap. J. (5:51). The Paris group proposed a modified volcanic theory for the origin of the lunar craters, rills and other topographic forms, which was later criticized by E. E. Barnard after he examined the planet with the 40-inch telescope. Barnard was then criticized by the Royal Astronomical Society for his criticism, and so on. One of the arguments in this debate had a deceptive simplicity: volcanoes produce water; there is no water on the moon; therefore the lunar craters are not volcanic. While most of the lunar craters are not volcanic, this is not a convincing argument because it neglects the problem of possible repositories for water. Very’s conclusions on the temperature of the lunar poles could have been read with some profit. Water there freezes out as frost. The other possibility is that water might escape from the Moon to space.