Hints respecting a New Theory on t he tilts of Comets. 233 



produced by the heat of the season, which would naturally 

 cause the wind to rush thither, with all its contents, and 

 with greater impetuosity. The coolness of the atmosphere 

 on elevated situations may be ascribed also to the evapora- 

 tion of the uppermost strata of the clouds, which accom* 

 panv the land winds. 



Many arguments I have dispensed with, which might 

 have been produced to elucidate and to establish my theory, 

 as they were chiefly such as could be collected from simple 

 inference, and from affirmative application of doctrines ad- 

 vanced before. 



I will only add, that both the sirocco and samiel may be 

 owing to similar causes as those which appear to be pro- 

 ductive of the pernicious, or rather disagreeable", effects of 

 our land winds. 



XLVIIF. Hints respecting a Ne?v Theory on the Orbits of 

 Comets. By Mr. W. Crane, of Edinburgh. 



To Mr. Tilloch. 



Sir, J. he following theory, for any thing I know, h 

 original: should it be deemed worthy of a place in the 

 Philosophical Magazine, its insertiou will much oblige 



Your humble servant, 

 W. Crane, 



Sept. 27, 1810. Student of Medicine, Edinburgh. 



** K:ist thou ne'er seen the comet T s flaming flight ? 

 The illustrious stranger passing, doubles wide 

 Heaven's mighty cape, and then revisits Earth." — Yoinier. 



The difficulties with which this intricate branch of astro- 

 nomy is surrounded, the short part of an orbit of a comet 

 that is visible to us, and the rarity of their appearance, have 

 given rise to innumerable theories, many of which have* no 

 sooner been advanced than they were immediately abau- 

 doned as erroneous. 



The school of Peripatetics assigned comets no place in 

 our planetary system, they only considered them as sub- 

 lunary things made up of the exhalations in the terrestrial 

 regions; which was the opinion of many, until Tycho Brahe 

 and Kepler proved by observation that they were beyond the 

 moon, and consequently not composed of terrestrial va- 

 pours : this was further confirmed by the observations made 

 by Cassini, of that seen in the year 1665, and of another 

 that appeared in April 1CS0. Cartesius thought them to 

 j he permanent bodies, like the planets, and to be constantly 



carried 



