Feb. 13, 1879] 



NATURE 



347 



Through the kindness of Mr. Mihie Home, I have been 

 favoured with the sight of letters addressed to you by 

 four eminent mineralogists, Dana of America, Ram- 

 melsberg of Berlin, Szabo of Buda-Pesth, and King of 

 Queen' s College, Galway. Szabo states that the notice 

 of your paper on the Feldspars, which appeared in Groth's 

 Zeitschrift fur Mineralogie, greatly interests him, and 

 makes him desirous of placing himself in direct commu- 

 nication with the author. Dana says, ' I have read your 

 paper on the Feldspars, in the Transactions of the Royal 

 Society of Edinburgh, with great satisfaction. Your 

 thorough method of work leads towards important results 

 of great geological, as well as mineralogical value.' 



" I have the satisfaction, in the name of the Council of this 

 Society, of presenting you with the Keith Medal. It is 

 hoped that this recognition of your labours will not be 

 without encouragement to you in the arduous researches 

 in which you are engaged." 



OUR ASTRONOMICAL COLUMN 



Tempel's Comet, 1867 II.— Now that Brorsen's comet 

 of short period is again under observation, the next comet 

 of the same class to be sought for, is that discovered by 

 Dr. Tempel at Marseilles, on April 3, 1867, which was 

 also observed at its next appearance in 1873 ; it is probable 

 there may be greater difficulty in recovering this object, 

 than appears to have been the case with Brorsen's comet, 

 the reason for which may be made clearer if we briefly 

 detail its history since the year 1867. Less than a month 

 after it was discovered in that year the deviation of the 

 orbit from a parabola became evident, and several of the 

 German astronomers, Prof. Bruhns, now Director of the 

 Observatory of Leipsic, in the first instance, deduced 

 elliptical orbits, with periods of between five and six 

 years. The most complete investigations on the motion 

 of the comet in this year were due to Dr. Sandberg and 

 Mr. Searle. The comet was observed by Dr. Julius 

 Schmidt at Athens till August 21, and the perihelion 

 passage baring taken place on May 23, a considerable 

 arc of the orbit was included within the limits of visi- 

 bility. Dr. Sandberg, after taking into accoxmt the eftect 

 of planetary perturbations during the comet's appearance, 

 foimd the period of revolution 2,080 days. On examining 

 the track of this body with reference to the orbits of the 

 planets, it was seen that near the aphelion it must 

 approach very near to the orbit of Jupiter, the least 

 distance being within 0*37 of the mean distance of 

 the earth from the sun, and from the position of 

 this great planet near the time of aphelion passage 

 of the comet early in 1870, it was obvious that 

 great perturbations in the elements of the latter must 

 ensue, and without at least an approximate knowledge 

 of their amount, there might be difficulty in recover- 

 ing the comet at its next return to perihelion. The first 

 publication of results in this direction was by Mr. W. E. 

 Plummer, from Mr. Bishop's observatory, Twickenham, 

 in February, 1873, followed shortly afterwards by par- 

 ticulars of similar independent investigations undertaken 

 by Dr. Seeliger, of Leipsic, and the late Dr. von Asten, 

 of Pulkowa. It was found that the effect of the attrac- 

 tion of Jupiter, which planet was only 0-32 distant from 

 the comet on January 20, 1870, caused a retrograde 

 change in the longitude of the node to the amount of 

 22^°, and increased the inclination of the orbital plane 

 to the echptic nearly 3= ; the period of revolution was 

 lengthened by more than three months, and the point of 

 nearest approach to the sun was removed further from 

 him by upwards of 0-2 of the earth's mean distance. 

 Changes in the elements to this amount would of course 

 entirely alter the track of the comet in 1873, but they had 

 been so closely determined, that immediately after receiv- 

 ing an ephemeris in which their effect was included, M. 

 Stephan re- detected the comet at Marseilles, and as early 

 as April 3, or five weeks before the perihelion passage. 



and it was observed until the last week in Jime. We 

 subjoin Dr. Sandberg' s elements for the two appeai>- 

 ances : — 



1867. 1873. 



Perihelion passage May 23*9204 G.M.T. May 9'oi34G.M.T. 



Long, of perihelion ... 236 9 24 237 38 42 



,, ascending node loi 10 10 78 44 39 



Inclination to ecliptic... 6 24 36 9 44 13 



Angle of excentricity... 30 38 39 27 30 58 



Log. semi-axis major ... 0*503658 0'5i7057 



Revolution 2080*1 days 2178*6 days. 



The longitudes are reckoned from the mean equinox of 

 the commencement of the respective years. The period 

 of revolution applies to the ellipse which the comet was 

 describing at perihelion passage. 



With regard to the length of the actual revolution, it is 

 certain that no very material perturbation can result 

 from known causes : Jupiter, the great disturber of the 

 cometary motions, was at almost his greatest possible 

 distance from the comet when the latter passed nearest 

 to his path about May, 1876. A recent investigation by 

 M. Raoul Gautier, of which, however, no details are yet 

 published, assigns a longer period of revolution corre- 

 sponding to the perihelion passage in 1873 than was 

 given by Dr. Sandberg, the difference being about loj 

 days, so that if the mean motion at the last appearance 

 does not, as M. Gautier implies, admit of exact deter- 

 mination, there will be an uncertainty in the date of the 

 approaching perihelion passage, which will necessitate a 

 pretty extended and careful search in order to detect the 

 comet. It belongs to the fainter class, and although in 

 1867 and 1873 it appeared \mder rather favourable cir- 

 cumstances for observation, and ^is likely to do so to a 

 certain extent this year, it has never been a good tele- 

 scopic object. When at its greatest intensity of light 

 early in May, 1867, its nucleus, which >vas stellar, had 

 not the brightness of a star of the ninth magnitude. At 

 the last observation at Athens, in that year the theoretical 

 intensity of light was 0*21, and the comet would have the 

 same degree of brightness about March 27 next, whether 

 we assume the time of perihelion passage (perturbation 

 neglected) from the orbit of Dr. Sandberg or M. Gautier, 

 but the uncertainty of position may probably delay its 

 rediscovery till some time later. We may hope that the 

 publication of the further results of M. Gautier, who 

 mentions being engaged on the calculation of perturba- 

 tions during the present revolution, will not be long 

 deferred. It is desirable the comet should be imder 

 observation as long as practicable at this return, since 

 the period being now nearly equal to half that of Jupiter, 

 the two bodies will come into proximity again towards 

 the month of November, 1881, though their mutual dis- 

 tance may not be less than 0*55. This will involve a 

 new, strict investigation similar to those undertaken in 

 1873, to enable the epoch of ensuing perihelion passage 

 to be ascertained. 



Using Dr. Sandberg' s orbit of 1873, the comet's place 

 at Greenwich midnight, on March 27, would be in R.A. 

 253°*9, N.P.D. io3°*7, or, if the perihelion passage be 

 assimied ten days later, which would more nearly accord 

 with M. Gautier' s calculation in R.A. 247''*o, N.P.D. 

 ioi°*o. 



The Intra-Mercurial Planet Question.— It 

 appears that this subject has lately engaged the atten- 

 tion of that excellent practical astronomer Dr. Oppolzer,. 

 of Vienna, who has commimicated to the Astronomische 

 Nachrichten some curious results of his examination of 

 the records of rapidly-moving dark spots upon the sun's 

 disk. His inquiry resolves itself simply into the conclus- 

 sion, that even introducing rather more extended data, 

 than were used by Leverrier, who, it will be remembered^ 

 foimd several possible periods of revolution for the hv'po- 

 thetical planet, they may all be represented so far as- 

 regards the necessity of a transit across the sun's disk on» 



