A. MATHEMATICS AND ASTRONOMY. 21 



PROFESSOR PLANTAMOUR's COMET. 



The papers have lately contained a sensational item in ref- 

 erence to an alleged communication from Professor Planta- 

 mour, of Geneva, to the effect that, according to his calcula- 

 tions, the earth, on the 12th of August, would come in colli- 

 sion with a very large comet, which in volume far surpasses 

 all that have hitherto appeared. Its approach is to be ren- 

 dered sensible by an extraordinary degree of heat, and a ca- 

 tastrophe is not to be avoided except by the deviation of the 

 rapidly approaching comet, produced by the attraction of 

 some other heavenly body within the scope of whose influ- 

 ence it may come. Our readers, however, need not be alarm- 

 ed by the prospect, as the fact is simply that about the 10th 

 to the 12th of August the earth will cross the meteoric stream 

 which was so conspicuous in 1866, and which has some inter- 

 esting relations to the orbit of the comet of 1862. It is not, 

 however, impossible that an unusually brilliant display of 

 meteors may be seen at this time, together with some extra- 

 ordinary auroral phenomena, and we presume that astrono- 

 mers and physicists will be prepared to take advantage of 

 the opportunity thus offered for spectroscopic and other re- 

 search. 15 A, February 17, 1872,213; and 3 A, February 17, 

 1872,137. . 



ZOLLNER ON THE NATURE OF COMETS. 



The American Journal of Science for June contains an ab- 

 stract of a work recently published by Professor Zollner upon 

 the " Nature of Comets," in which, starting from the well- 

 known fact that water, mercury, and many other substances, 

 even in the solid state, give off vapor of a certain amount, 

 though of very low tension, and inferring from the charac- 

 teristic odors of the metals that they also, even at very low 

 temperatures, are constantly giving off vapor, though of an 

 amount too small to be recognized by any of the tests yet 

 employed in science, it follows that a mass of matter in space 

 will ultimately surround itself with its own vapor, and the 

 tension of the latter will depend upon the mass of the body 

 that is, upon its gravitative energy and the temperature. 

 If the mass of the body is so small that its attractive force is 

 insufficient to give the enveloping vapor its maximum ten- 



