which hitherto has leen unobserved ly Philosophers . 191 



with a less quantity of atmosphere ; and the consequence would 

 be, that the heat of the sun would never overpower them, even 

 where it was greatest, for want of a denser atmosphere; and when 

 they were furthest from him, his faint heat added to their own 

 would give them a healthy temperature, equal to ours in the win- 

 ter time. With respect to hght, the effect would be precisely 

 the same; for though the atmosphere does not magnify the hea- 

 venlv bodies, it produces a great deal of additional light by 

 bringing down to us a number of diverging rays, that would 

 otherwise pass away from us, as well as by compressing them to- 

 gether and making them brighter. Now if the comets had no 

 light of their own, their day, when at a distance from the sun, 

 would either not ecjual the brightness of our moonlight; or else, 

 when they were near, the light of their day would be intolerable. 

 Bv giving them thus a light of their own, equal perhaps to our 

 summer twilight, with a small quantity of atmosphere, the ad- 

 dition of the sun's light to their oWn when they are at a distance, 

 may about equal our light in winter; and, when they are close to 

 him, may be no more than what we have in summer. By this 

 rule, the comets would never be in perfect darkness, their nights 

 would be always e({ual to our twilight ; with this exception, they 

 would liuve the same light and heat that we have, and perhaps 

 every other accommodation, whilst their philosophers, in the 

 course of their travels, would have o]>|Jortunities of making dis- 

 coveries that must ever be hid from our eyes. 



Having converted the ominous and ill-boding comet into a 

 comfortable habitation for man, I now come to show what the 

 tail is, and the cause of its appearing always opposite the sun. I 

 consider the tail to be nothing else than a continuation of the 



to make a sensible alteration in the sun's angle, it is very possible that the 

 increa.sed number of rays would more than equal the diminution of their 

 heat. Mercury, for instance, is only thirty-tvvo millions of miles from the sun ; 

 and by travelling thirty-two millions of miles furtlier, he would have twice as 

 many rays striising upon him as Mercury received ; whereas if he was at tils' 

 Georgium Sidus, he must travel eighteen hundred millions of miles in order 

 to double the quantity of rays: it is probable, therefore, that long before he 

 arrived at this planet, the diminution of heat would be a great deal more 

 than could be made up by the accession of numbers, and the Georgum Sidus 

 would want an additional quantity of atmosphere to make up for the defi- 

 ciency. 



The place in the heavens where the sun's heat is strongest must alway.' 

 rest upon mere conjecture, because we have no means of ascertaining how 

 much of the sun's heat his rays lose in a given distance : but there is strong 

 ground to believe that the ;iun's greatest heat is not near himself; because, 

 in Sir Isaac Newton's time, a comet passed within the length of his dia- 

 meter of him without appearing to su.Ter any damage ; wlicreas, had tho 

 sun's heat, in that place, been so strong as Sir Isaac supposed, tiie comet 

 must have been burned to a tinder, if he had been formed of any materials of 

 which wc have any knowledge. 



coma. 



