Chap. 1 4.] Principles of Aerojlatkn. 513 



This dreadful cataftrophe feems to have contributed 

 to put an end to thefe experiments. Mr. Baldwin, 

 of Cheder, however, afcended from that city in the 

 month of September, in the fame year, and has pub- 

 lilhed a very accurate and curious account of his ob- 

 fervations during his voyage. In his afcent he ob- 

 ferved, that the lowed bed of vapour neareft the earth 

 appeared like pure white clouds in detached pieces, 

 which feemed to increafe as he rofe. They prefently 

 coalefced, and formed, as he fays, f a fea of cotton, 

 tufting here and there by the action of the air in the 

 imdifturbed part of the clouds.' The whole foon be- 

 came an extended white floor of cloud j above which, 

 at great and unequal diftances, he obferved a vaft af- 

 femblage of thunder clouds, each parcel confifting of 

 whole acres in the denfeft form j he compares their 

 form and appearance to the fmoke of cannon, only 

 denfer, and fomewhat refembling vaft mafles of fnow. 

 Some clouds had motions in flow and various direc- 

 tions, forming a fcene upon the whole truly flupendous 

 and majedic. 



The principles on which balloons afcend in the at- 

 mofphere will, after what has been dated, be eafily 

 underftood. It is a well known rule in hydrodatics, 

 that when a body is immerfed in any fluid, if its weight 

 is lefs than an equal bulk of that fluid, it will rife to 

 the furface, but if heavier it will fink, and if equal it 

 will remain in the place where it is fird dationed. On 

 this principle, fmoke or vapour afcends in the atmo- 

 fphere, and heated air in that which is colder. That 

 heated air will afcend is eafily proved, by bringing a 

 red-hot iron under a fcale of a balance, which will in- 

 ftantly afcend, becaufe the hot air, being lighter than 

 that which is colder, afcends, and drikes the bottom, 



VOL. I. L 1 and 



