PORTION OP THE COSMOS. COMETS. 397 



vapeurs et (Tun noyau s'accroissant par la condensation de 

 1' atmosphere qui Fenvironne, les cometes sont etrangeres 

 au systeme planetaire" ( 647 ). 



I have already called attention, in the first volume of my 

 work ( 648 ), to the fact that comets combine the smallest 

 mass with the occupation of the largest space within the solar 

 domain ; they also exceed all other planetary cosmical bodies 

 in number of individuals; the calculus of probabilities, 

 based on the assumption of an equable distribution of 

 orbits, limits, nearness to the Sun, and possible continued 

 invisibility, leads to our inferring the existence of many 

 thousands. I purposely exclude from such comparative 

 considerations "aerolites," or "meteoric asteroids," because 

 much obscurity still prevails respecting their nature. We 

 must distinguish among comets those whose orbits have 

 been computed by astronomers from those of which we 

 possess, in some cases, only incomplete observations, and in 

 others, mere notices in chronicles. As, according to Galle's 

 latest exact enumeration to the year 1847 inclusive, 178 

 comets had been calculated, we may very well continue to 

 take as the number of comets which have been seen, 

 including those of which we merely possess notices, a rough 

 total of from six to seven hundred. When the comet of 

 1682, announced by Halley, reappeared in 1759, it was 

 regarded as something very remarkable that three comets 

 should be visible in the same year. Now, so animated is 

 the examination of the celestial vault, and from so many 

 points of the earth's surface at the same time, that in each 

 of the years 1819, 1825, and 1840, four comets were seen 

 and computed ; in 1826, five ; and in 1846, even as many 

 as eight. 



