Pec. 20, 1877] 



NATURE 



149 



The average distance between the solar lines in the 

 green, which have not yet been identified, is about 4"4, or 

 more than fourteen times the difference between the 

 centre of the oxygen line and the corresponding solar line. 

 The average distance between the non-identified lines 

 near O « is 4'9, or about twenty-nine times the correspond- 

 ing difference. In judging, however, of the value of the 

 evidence, I should like the reader to leave the line S out 

 of account. Although the agreement seems perfect, 1 

 have not the same confidence in the correctness of the 

 wave-length as I have with the other lines. The line /3 is 

 weaker than the others, and the error of observation may 

 be a little larger than with a and y, which will, I think, be 

 found correct to the decimal place. 



Let me point out in a few words the importance of the 

 results obtained. The compound line spectrum of oxygen 

 can only exist under a limited range of physical con- 

 ditions. It is broken up at a higher temperature into the 

 elementary line spectrum, and at a lower temperature it 

 tumbles together into a continuous spectrum. During its 

 existence its lines may be subject to variations owing to 

 pressure. The spectrum of oxygen is therefore pre-emi- 

 nently fitted to be at once the pressure gauge and ther- 

 mometer of the sun. We cannot at the present moment 

 give the exact temperature of the points at which the 

 changes take place ; but we can say with certainty why 

 it is that the line spectra of many metalloids are not 

 found reversed in the sun, for the temperature which gives 

 these line spectra is higher than that which gives the 

 compound line spectrum of oxygen, and therefore higher 

 than that of the reversing layer of the sun. Conse- 

 quently we must look for their band spectra and not for 

 their line spectra. The same may be true for the spectra 

 of some of the heavier elements like gold, silver, and 

 platinum, which have not yet been discovered in the sun. 

 The continuous spectrum of the base of the corona is 

 most likely the continuous spectrum of the cooler oxygen. 



As the science of spectroscopy advances we shall be 

 able to determine the physical conditions which exist on 

 the surface of the sun with as great a degree of certainty 

 and a much smaller degree of discomfort than if we were 

 placed there ourselves. I hope that this communica- 

 tion will prove to be a step in that direction. All my 

 experiments were made in the Cavendish Laboratory. 



Arthur Schuster 



St. John's College, Cambridge, November 30 



OUR ASTRONOMICAL COLUMN 



Jupiter's Satellites.— Amongst the recorded pheno- 

 mena connected with the motions of the satellites of 

 Jupiter are several notices of observed occultations of one 

 satellite by another, and of small stars by one or other of 

 the EateUites. The following cases may be mentioned : — 

 On the night of November i, 1693, Christoph Arnold, 

 of Sommerfeld, near Leipsic, observed an occultation of 

 the second satellite by the third at loh. 47m. apparent 

 time. On October 30, 1822, Luthmer, of Hanover, 

 witnessed an occultation of the fourth satellite by the 

 third at 6h. 55m. mean time. 



Flaugergues, writing to Baron de Zach, from Viviers, 

 on November 18, 1821, says : " I begin with an observa- 

 tion, very useless, no doubt, but extremely rare, for I have 

 not found a similar one in the collections of astronomical 

 observations which I have' examined ; i.e., the occultation 

 of a very small star by the third satellite of Jupiter." He 

 proceeds to mention that on August 14, 1 821, he repaired 

 to his observatory very early to observe an eclipse of this 

 satellite, and having looked at Jupiter with the telescope, 

 he remarked a very small star near the third satellite. 

 The satelhte approached this star, and at ih. 47m. 

 sidereal time, it appeared to touch it, and at ih. 56m. 52s. 

 it was not possible to distinguish the star — it had dis- 

 appeared. The satellite became fainter and disappeared 



in its turn at ih. 59m. los. sidereal time, on August 13, 

 or i6h. 30m. 8"5s. mean time at Viviers. The sky was 

 perfectly clear, and Flaugergues considered his observa- 

 tions very exact. He adds that he continued to observe 

 for a long time after the immersion of the satellite, hoping 

 to see the star reappear, but he could not again distin- 

 guish it ; the twilight had much increased, and small stars 

 in the neighbourhood of Jupiter were soon effaced. 



There is a similar observation by Mr. G. W. Hough, at 

 Cincinnati Observatory, communicated in a letter to Dr. 

 Brunnow, when Director of the Observatory at Ann Arbor, 

 Michigan, and published in his "Astronomical Notices" 

 Mr. Hough states that on March 28, i860, he witnessed 

 the end of an expected occultation of a star 9*5 mag., by 

 Jupiter, and the occultation of the same star by the first 

 satellite. When first seen it was distant from the limb 

 of the planet about one diameter of the satellite, or one 

 second of arc, so that the real separation had taken place 

 about six minutes before (or about 8h. 9m. sidereal time), 

 though he was not able to see it. At loh. 27m. sidereal 

 time the star was occulted by the first satellite and re- 

 mained invisible eight minutes. Mr. Hough further says 

 that the star is found in the " Redhill Catalogue," an 

 obvious oversight ; it would appear to be No. 1630 of 

 Zone -f 22° in the DurcJwiiisterung, a. star of 9*3 m. the 

 approximate place of which for 1855 was in R.A. 7h. 8m. 

 5s., N.P.D. 67°3'-3. 



DoNATi's Comet of 1858,— This comet which attained 

 so great a celebrity in the autumn of 1858, makes a very 

 close approximation to the orbit of Venus near the 

 descending node, and it may be reasonably inferred that 

 the actual form of its path round the sun may be due to a 

 very near approach of the two bodies at some distant 

 epoch. The discussion of the totality of observations was 

 undertaken some years since by Dr. von Asten, who has 

 published his results in a dissertation entitled " Deter- 

 minatio orbitas grandis cometce anni 1858, e cunctis 

 observationibus." The comet was discovered by Donati 

 on June 2, and was observed until the beginning of March, 

 1859, at the Cape of Good Hope and at Santiago de 

 Chile ; consequently the observations extended over a 

 very wide arc of the orbit, and there have been very few 

 cases where careful discussion could be expected to lead to 

 more reliable results. The period of revolution deduced 

 by Dr. von Asten is 1,880 years, and there is a high pro- 

 bability that this does not differ materially from the true 

 one, applying to the time of the comet's appearance. 

 Prof. Hill, of Washington, also by a complete inves- 

 tigation, obtained a somewhat longer period, but the 

 general character of the orbit remains the same. Em- 

 ploying Dr. von Asten's elements, it will be found that in 

 heliocentric longitude 343°7, the distance of the comet 

 from the orbit of Venus, is only 0*0047 of the mean dis- 

 tance of the earth from the sun. In 1858 the two bodies 

 came into pretty near proximity, their mutual distance on 

 October 17 being o'o88. It has been mentioned above 

 that the point of closest approach of the orbits of the 

 planet and comet is situated near the descending node ; 

 the opposite node falls in the region of the minor planets. 



The Observatory of Lyons. — The Bulletin Hebdo- 

 viadaire of the French Scientific Association reports that 

 M. Andre is actively employed in the establishment of 

 this new astronomical institution and is energetically 

 supported by the Government. M. Raphel Bischoffsheim, 

 the munificent donor of the meridian circle, lately mounted 

 at the Observatory of Paris, has also intimated his inten- 

 tion to present the Lyons Observatory with its funda- 

 mental instrument, a meridian- circle of dimensions but 

 slightly inferior to those of the circle, for which the 

 Observatory at Paris is indebted to him. It will also be 

 constructed by Eichens. The Paris meridian-circle is 

 intended to replace the instruments of Gambey, which are 

 now placed in one of the saloons of the institution with 

 other instruments which have seen their day. M. Wolf 



