7«/)/ 27, 1876] • 



NATURE 



277 



OUR ASTRONOMICAL COLUMN 



De Vico's Comet of Short Period. — According to 

 the limits for the value of the mean diurnal motion of this 

 comet when it was last observed, in 1844, assigned by 

 Prof. Briinnow from his later researches, the results of 

 which are published in the Astronomical Notices issued 

 during his direction of the Observatory of Ann Arbor, 

 Michigan, it would appear that in the absence of any 

 great perturbation a perihelion passage may be expected 

 to occur some time in the twelve months following the 

 beginning of December next, and those who occupy 

 themselves in searching for comets might advantageously 

 institute during that interval a systematic examination of 

 the parts of the sky in which the comet must be situate 

 according to different suppositions as to the date of 

 arrival at perihelion. 



The comet of De Vico is most favourably placed for 

 observation when the perihelion falls about Sept. 4, in 

 which case it approaches the earth within o'2 of our 

 mean distance from the sun. It follows therefore that in 

 1844, when the comet was in perihelion about midnight 

 on Sept. 2, the conditions were nearly at their best. The 

 comet was detected at Rome on August 22, and was 

 observed by O. Struve at Pulkowa, till Dec. 31. In a 

 masterly discussion by Prof. Briinnow, entitled Memoire 

 stir la Co7nete Elliptiqne de De Vico, which gained the 

 prize offered by the Royal Institute of the Netherlands, 

 the elements for 1844 are determined by the most refined 

 methods, and are accurately perturbed not only to the 

 next return in 1850, when from the position of the comet 

 in the heavens there appeared no possibility of its being 

 observed, but to the second return in 1855, when the 

 perihelion is fixed to August 6, ephemerides to facilitate 

 Its re-discovery being added to the memoir. From what- 

 ever cause, however, the comet was not found in 1855. 



The mean motion finally adopted in Briinnow's memoir 

 for the perihelion passage in 1844 corresponds to a revo- 

 lution of I996"3 days. In the subsequent calculations to 

 which reference is made in the Ann Arbor Notices, he 

 finds a value which diminishes the period of revolution to 

 1994*0 days, and, as regards the probable error of this 

 determination of the amount of daily sidereal motion 

 (649''"936), he shows that his work rather tends to exclude 

 a greater one than 2". Nevertheless he particularly 

 insists that too much stress should not be placed on this 

 indication, pointing out the possible influence of a small 

 but variable error in the sun's places, which were taken 

 from Carlini's Tables, and likewise the effect of variation 

 in the form of the comet during the time it was under 

 observation, upon the deduced positions. It does not 

 appear upon what authority Briinnow assumes the reality 

 of material changes in the aspect of the comet. The 

 writer of these lines had the comet under frequent obser- 

 vations particularly after the middle of October, when, as 

 it was receding from the earth, variation of figure by 

 influencing the judgment as to the point to be observed 

 would have had most effect, and well remembers that 

 even to the last week in December, when it had become 

 little more than a glimpse-object with 7 inches aperture, 

 there was still an extremely minute nuclear point, which, 

 with a larger instrument, would admit of very accurate 

 bisection. The comparison with the Pulkowa observations 

 {Memoire. p. 29) affords no evidence of any effect of the 

 kind suggested by Briinnow. 



Now there is one point, hitherto it is believed un- 

 noticed in the astronomical periodicals, which bears upon 

 the non-recovery of the comet of late years. Briinnow 

 drew attention to the close approximation of the orbit of 

 De Vico's crmet to the orbit of the planet Mars at two 

 points falling near 42° and 287° of heliocentric longitude. 

 If we adopt his later elements, we find that at the first 

 point the distance between the twc^orbits was 0-0226, and 

 at the latter point 0*0104, distances which, as Briinnow 



remarks, are " assez petites, pour produire des perturba- 

 tions sensibles, quelque petite que soit d'ailleurs la masse 

 de la plan^te perturbatrice ;" and it is to be borne in 

 mind that the above distances, small as they are, may 

 have been diminished very sensibly by the effect of accu- 

 mulated perturbation since 1855, beyond which we have 

 no calculation of the effects of planetary attraction. If 

 the mean diurnal motion in 1855 were as large as 652""o5, 

 a value considerably within Briinnow's suggested limits, 

 the comet might have come into extremely close prox- 

 imity to Mars at the end of August, 1866, in about 42°*3 

 heliocentric longitude. 



While, however, the above appears a certainly possible 

 contingency, it is not, perhaps, necessary to suppose the 

 existence of any unusual cause for the non-recovery of 

 the comet. As occurs with most of these bodies, there 

 are certain periods of the year at which observation would 

 be impracticable ; in the case of the comet of De Vico, 

 this disadvantageous period would fall chiefly in the first 

 four months of the year, the perihelion point then falling 

 on the opposite side of the sun to the earth, and the incli- 

 nation of orbit being very small. How far this may 

 bear upon the question may be judged from the fact 

 of there being ' no record of this comet having been 

 observed between the year 1678, when Le Verrier iden- 

 tifies it with the comet discovered by Lahire at Paris, and 

 the re-appearance in 1844 ; and it is worthy of remark 

 that the perihelion passage in 1678 fell only one week 

 earlier than the date which may be considered the most 

 favourable. 



A more particular examination of the comet's track in 

 the heavens at different periods of the year is deferred 

 for a future column. 



MiRA Ceti. — The minimum for 1876, calculated by 

 Argelander's formula of sines from the epoch of Schon- 

 feld's last catalogue, i.e., by applying the same pertur- 

 bations to minimum as to maximum, falls September i '2, 

 and may therefore be observed under favourable circum- 

 stances. There are comparatively few good deter- 

 minations of the minima epochs, or of the magnitude of 

 the star at these times, which will justify a hint that it 

 should be watched on this occasion. 



RESOURCES OF SERVIA AND BOSNIA 



npHE small extent of country upon which the eyes of 

 -^ Europe are now centred lies too far out of the 

 beaten tracks of travellers for much to be generally known 

 as to its capabilities or natural resources ; nevenheless 

 the country is described in the few existing works as 

 being very fertile, and the soil might be made much more 

 productive were it not for the idle and dirty hab.ts of the 

 people. In these days of " Special Correspondents," the 

 breaking out of a war, even in the remotest parts of the 

 world, is a signal for the dispatch of men of observation, 

 whose duty it is to chronicle the movements of the 

 opposing parlies, and, in some cases — we wisii it were 

 more often so — to give us glimpses into the habits of the 

 people and the natural features of the country. Thus, we 

 may in the course of a few weeks learn from the public 

 press more about these matters in connection with the 

 small districts now at war with Turkey than we are able 

 to gain from books. The mines of Servia and the 

 forests of Bosnia are two of the principal sources of 

 revenue to the countries. Both iron and copper can be 

 obtained, not only in large quantities, but also of ex- 

 cellent quality. The best Bosnian iron resembles that of 

 Sweden, and is largely used in the manufactories of 

 Gratz, in Styria ; quantities also pass into Dalmatia and 

 Servia. These mines are mostly worked by English 

 companies under concessions from the authorities. In 

 the forests are several species of oak, including the ever- 

 green, or Holm Oak {Quercus Ilex), the Turkey Oak 

 {Q. Cerris), Q. ^Egilops, Q. infectoria, and others. The 



