J*N T KLMATiCS. 1 6-1 



one of the scales of a balance, by means of a thread; 

 and having properly counterpoised it by weights 

 put into the opposite scale, apply the flame of a 

 candle underneath, and you will instantly see the 

 cone rise; and it will not be brought into equili- 

 brium with the other, but by a much greater 

 weight than those who have never seen the ex- 

 periment would believe. 



If the magnitude of a balloon be increased, its 

 power of ascension, or the difference between the 

 weight of the included air and an equal bulk of 

 common air, will be augmented in the same pro- 

 portion. For its thickness being supposed the 

 same, it is as the surface it covers, or only as the 

 square of the diameter. This is the reason why 

 balloons cannot be made to ascend, if under a 

 driven magnitude, when composed of cloth, or ma- 

 terials of the same thickness. 



In the year I76G, Mr. Cavendish ascertained the 

 weight "and other properties of inflammable air, 

 determining it to be at least seven times lighter 

 than common air. Soon after which it occurred 

 to Dr. Black, that, perhaps, a thin bag, filled with 

 inflammable air, might be buoyed up by the com- 

 mon atmosphere, and he thought of having the 

 allantois of a calf prepared for this purpose; but 

 his other avocations prevented him from prosecuting 

 the experiment. The same thought occurred, 

 some years after, to Mr. Cavallo, and he has the 

 honour of being the first who made experiments 

 on the subject. He first tried bladders, but the 

 thinnest of these, however, well scraped and pre- 

 pared, were found too heavy; he then tried. 

 Chinese paper, but that proved so permeable, that 

 the inflammable air passed through it like water 

 through a sieve. His experiments, therefore, made 



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