32 On Air Balloons. 



plicate proportion, will be eight times as large, and conse- 

 quently eight times as heavy as a globe of one foot diameter ; 

 so that the superfices of the larger over the smaller will be as 

 four to one, and the solidity as eight to one. All of which may 

 be easily proved by experience, of which he gives numerous 

 examples in his own experiments with glass globes filled with 

 water, or divested of the air ; and then proceeds to calculate to 

 what dimensions copper globes may be made, light enough to 

 weigh less than the air they are capable of containing; and 

 comes to the conclusion, by figures, that they may be conve- 

 niently made to contain 718 lbs., and that when the air is 

 extracted they will weigh 410 lbs. loz. less than before^ and 

 consequently be capable of lifting two or three men. His 

 method of procuring the vacuum is as follows: — He fills his 

 globes of copper, resting on a stage, with water, by means of a 

 plug at the top, and by opening a stop-cock lets it out through 

 a long tube into a vessel of water below, and, unscrewing the 

 tube, his globe is in a condition to ascend, but is restrained by 

 cords ; and four or more of these globes are bound together, 

 according to the weight of the vessel to be elevated from his 

 balloon ; to which is attached the boat, furnished with a mast 

 and sail, capable of being turned in any direction, which is to 

 be accommodated with an anchor, also, when proposed to be 

 stationary. 



And now, says the author, ^' I can hardly help smiling to 

 myself, to think that it seems to be a fable not less incredible 

 than that which issued from the voluntary and wild fancies of 

 the head of Lucian ; while, on the other hand, I know that I 

 have not erred in any of my proofs, having conferred on the 

 subject with numerous well-informed men, who could not dis- 

 cover any errors in my calculations, and who only desired to 

 behold the experiment, and see the vessel ascend ; which I 

 would willingly have gratified them with, previously to publish- 

 ing my invention, if the religious poverty I profess had per^ 

 mitted me to expend one hundred ducats, ivhich would be more 

 than enough to satisfy a curiosity so agreeable. Hence, I must 

 request any of my readers who may be induced to try this 

 experiment to favour me with an account of their success ; 

 since, should any errors be committed in the operation, I may 



