28 



On the prefent State of AeroJIailon, 



fill attempts to render aerial navigation of fervice to man- 

 mind, ought to be no argument for caufing it to be difcoun- 

 tenanced by men of fenfe, or prohibited bv civil authority; 

 as experiments in any art, however multiplied, if not well 

 adviied and conducted, cannot be expelled to fulfil the erro- 

 neous expeftations of their projeftors. 



To affift the artift in conllruding his aeroftatic apparatus, 

 it may not be amifs to fubjoin the following data : — The dia- 

 meter is to the circumferclice of a fphere as i to 3', or as 

 I to 3" 14:5. The circumference multiplied by the diameter 

 gives the furface of the fphere in fquare dimenfions, and i-6lh 

 of the furface multiplied by the diameter, or the cube of the 

 diameter multiplied by 0*5236, gives the capacity or folid 

 contents in cubic meafure. By the weight of a fquare foot 

 of the envelope may be found the weight of the whole bag, 

 allowing for the feams ; and to find the power of afcenfion, 

 fubtraft the weight of the bag and inclofed air from the 

 weight of an equal bulk of atmofpheric air *, and the quo- 

 tient will give the power which the balloon will exert to rife, 

 which (during its afcent) will decreafe till the equilibrium 

 between the two is reftored ; and this point may be nearly 

 afcertained by recollefting that the denfity of the atmofphere 

 decreafes in the geometrical ratio, and is reduced to half an 

 atmofphere at three miles and a half from the earth's fur- 

 face f. If a balloon with its annexed apparatus weighs there- 

 fore, at the inftant of afcent, but half an equal bulk of com- 

 mon air, it will rife to three miles and a half perpendicular 

 height; but, as the denfity of the inflammable air decreafes 

 alfo in the ratio of the diminifliing preflure of the furround- 



* A cubic foot of water weighs 1000 ounces avoirdupoile : and as the 

 •lenfity of air to water is as i to 800, this will be li ounce for every cubic 

 foot of atmofpheric air : the weight of inflammable air varies according to 

 its purity, fo as to be even 17 times lighter than common air ; but in th^ 

 grofs way, for aeroftatic purpofes we mult not expedt to obtain it more 

 than eight or ten times lighter than atmofpheric air. 



f Agreeably to the annexed table : 

 At miles 



3^ 







