22 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



1684 that have come down to us were made during two 

 weeks at Rome by Bianchini ; and in order to derive from 

 these the best possible results, Neugebauer lias reduced them 

 all anew, by using the best materials available, he having ac- 

 cess to original letters and drawings still in existence. The 

 observations made by Bianchini were of the simplest kind ; 

 for instance, he would hold a stretched thread in such a po- 

 sition that, while it covered some one of the known fixed 

 stars, it nearly covered the comet itself, whose position, rela- 

 tively to the ends of the thread, was then estimated by the 

 eye. Other and more exact observations were made with 

 the help of rude instruments. The relative positions of the 

 comet, as deduced by great labor, in general seem to be trust- 

 worthy to within a few minutes of arc, and Neugebauer's ele- 

 ments of its orbit are not greatly different from those given 

 by Halley. It follows, as the most interesting result of the 

 investigation, that on the 18th of June, 1684, the distance of 

 the comet from the earth was only the hundredth part of the 

 distance of the earth from the sun, being, in fact, only the 

 thirtieth part of the distance of the earth from Coggia's comet 

 on the 21st of July, 1874, when it was nearest the earth. It 

 seems, therefore, that the orbit of the comet of 1684 approach- 

 es more nearly to the orbit of the earth than almost any 

 other knowm comet, and that under favorable circumstances 

 we shall be justified in expecting some meteoric display year- 

 ly about the 18th of June, at which time the earth annually 

 comes into the plane of this comet's orbit. Inaugural Dis- 

 sertation, J3reslau,l&'73. 



THE PHENOMENA OF COMETS. 



As the result of a suggestive paper by Faye on the forms 

 of comets, he states that he has been led to conclude with 

 perfect certainty that cometary phenomena reveal to us in 

 the heavens the existence of a second force totally different 

 from attraction, and capable of playing an important part, 

 and producing before our eyes gigantic phenomena ; that, 

 with great probability, this force is nothing less than the 

 repulsion due to heat. In order to demonstrate experiment- 

 ally the existence of such a repulsion (which is mathematical- 

 ly deducible from the dynamic theory of gases), he advises 

 the following arrangement: Ajar of very rarefied air is il- 



