On Air Balloom, 3i" 



construct skips ^ which shall be sustained only by the air^ and 

 be conducted by means of a mast and sail — the practicability 

 of which is demonstrated , he thus proceeds — 



" The human intellect is not satisfied with the above inven- 

 tions, but proceeds to improve on them by a method, by which 

 meny like birds, should fly in the air ; and probably the story of 

 Vcedalus may not be fabulous, since we are told, as a certainty, 

 that a person (whose name I do not remember) in our times, 

 by a similar method, passed across the lake of Perugia, and 

 afterwards, in attempting to alight on the ground, let himself 

 descend with such impetuosity, that it cost him his hfe. No 

 one, however, has hitherto thought it possible to fabricate a ship 

 to pass through the air, as one does that is sustained by the 

 water, since it has been judged to be impossible to construct a 

 machine lighter than the air itself, which would be necessary to 

 produce the desired effect. 



^* Hence, I, whose genius ever led me to recover difficult 

 inventions, after long study, conceive that I have obtained my 

 object of constructing a machine lighter than air, which not 

 only, by its own levity, can sustain itself in air, but be capable 

 of supporting men, and any given weight ; neither do I fear to 

 be deceived, since the whole can be demonstrated by certain 

 experience, and by an infallible demonstration from the 11th 

 book oi Euclid, received as such by every mathematician. Let 

 us, therefore, lay down certain propositions, from whence may 

 be deduced a practical method of fabricating such a vessel, 

 which, if it does not merit, like that of Argus, to be placed 

 among the stars, will of itself be able to sail towards them." 



He then proceeds to describe in what manner he found the 

 weight of the air, by a method then in use, and which is after- 

 wards more fully detailed, when describing the practical part of 

 his machine ; and after going through a long series of calcu- 

 lations, founded on the principles laid down by Euclid, in his 

 11th and 12th books, to prove that the superfices of a ball or 

 sphere increases in the duplicate ratio of its diameter, — as, for 

 example, that a globe whose diameter is double that of another — 

 say one of one foot, and another of two — the superfices of the 

 globe of two feet will be four times as large as that of one, and 

 that the solid body of the globe, if two feet increased in a tri- 



