48 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



carbon, chiefly the dioxide as their characteristic gases, in- 

 stead of hydrogen. Second, the proportion of carbon di- 

 oxide given off is much greater at low than at high temper- 

 atures, and is sufficient to mask the hydrogen in the spec- 

 trum. Third, the amount of gases contained in a large 

 meteorite, or cluster of such bodies serving as a cometary 

 nucleus, is sufficient to form the train as ordinarily observed. 

 Fourth, the spectrum of the gases is closely identical with 

 that of several of the comets. We may, then, he states, con- 

 sider a comet merely as a meteorite of considerable magni- 

 tude, or a swarm of many such of lesser size, containing 

 large quantities of carbon dioxide, with some carbonic oxide 

 and hydrogen, and giving off this gas under the influence of 

 solar heat. The gaseous substance in streaming away forms 

 the train which is visible, partly by reflected sunlight, and 

 partly by its own light, due to some molecular or electrical 

 action which causes it to give the spectrum of the carbon 

 compounds. The loss of the gaseous contents readily ex- 

 plains the loss of the tail and diminution of brightness, ob- 

 served in the case of several comets in their successive rev- 

 olutions. Sillimcui's Journal, July, 1875, 48. 



THE DISTRIBUTION OF COMETARY ORBITS. 



Guillemin calls attention in his new work on comets to a 

 feature in the distribution of the orbits of these bodies, which 

 consists especially in the fact that there are special regions 

 of the heavens in which the cometary aphelia are more thick- 

 ly crowded together than in other regions. Basing his stud- 

 ies upon those of Hoeck, of Utrecht, he places the region 

 within which the least number of cometary aphelia is found 

 in the sector comprised between the ecliptic and a circle 

 inclined thereto at an angle of about 35, and cutting it in 

 the longitudes 95 and 243. In explanation of this singular- 

 ity, Hoeck suggests that if the point toward which the solar 

 system is moving in its great motion of translation occupied 

 the middle of this sector, it would follow that the comets 

 coming from this region would have greater difficulty than 

 any others in following and rejoining the sun. But the 

 direction of the movements of the solar system is such that 

 it does not favor this explanation. Guillemin suggests, 

 therefore, that possibly this sector corresponds to a region 



