240 Things not generally Known. 



THE COMET OF DONATI. 



While this sheet was passing through the press, the attention 

 of astronomers, and of the public generally, was drawn to the 

 fact of the above Comet passing (on Oct. 18) within nine mil- 

 lions of miles of the planet Venus, or less than yfo-ths of the 

 earth's distance from the Sun. " And (says Mr. Hind, the as- 

 tronomer), it is obvious that if the comet had reached its least 

 distance from the sun a few days earlier than it has done, the 

 planet might have passed through it ; and I am very far from 

 thinking that close proximity to a comet of this description 

 would be unattended with danger. The inhabitants of Venus 

 will witness a cometary spectacle far superior to that which 

 has recently attracted so much attention here, inasmuch as the 

 tail will doubtless appear twice as long from that planet as 

 from the earth, and the nucleus proportionally more brilliant." 



This Comet was first discovered by Dr. G. B. Donati, astro- 

 nomer at the Museum of Florence, on the evening of the 2d of 

 June, in right ascension 141 18', and north declination 23 47', 

 corresponding to a position near the star Leonis. Previous to 

 this date we had no knowledge of its existence, and therefore 

 it was not a predicted comet ; neither is it the one last ob- 

 served in 1556. At the date of discovery it was distant from 

 the earth 228,000,000 of miles, and was an excessively faint ob- 

 ject in the largest telescopes. 



The tail, from October 2 to 16, when the comet was most 

 conspicuous, appears to have maintained an average length 

 of at least 40,000,000 miles, subtending an angle varying from 

 30 to 40. The dark line or space down the centre, fre- 

 quently remarked in other great comets, was a striking cha- 

 racteristic in that of Donati. The nucleus, though small, was 

 intensely brilliant in powerful instruments, and for some time 

 bore high magnifiers to much greater advantage than is usual 

 with these objects. In several respects this comet resembled 

 the famous ones of 1744, 1680, and 1811, particularly as re- 

 gards the signs of violent agitation going on in the vicinity of 

 the nucleus, such as the appearance of luminous jets, spiral 

 offshoots, &c., which rapidly emanated from the planetary point 

 and as quickly lost themselves in the general nebulosity of the 

 head. 



On the 5th Oct. the most casual observer had an opportu- 

 nity of satisfying himself as to the accuracy of the mathematical 

 theory of the motions of comets in the near approach of the 

 nucleus of Donati's to Arcturus, the principal star in the con- 

 stellation Bootes. The circumstance of the appulse was very 

 nearly as predicted by Mr. Hind. 



The comet, according to the investigations by M. Loewy, 



