l6S ON AERIAL NAVIGATION. 



provided the usual plan of a large boiler be given up, and 

 the principle of injecting a proper charge of water into a 

 mass of tube-,, forming the cavity for the fire, be adopted 

 in lieu of it. The strength of vessels to resist internal 

 pressure being inversely as their diameters, very slight me- 

 tallic tubes would be abundantly strong-, whereas a large 

 boiler must be of great substance to resist a strong pressure. 

 The following estimate will show the probable weight of 

 such an engine with its charge for one hour. 



lb. 



Thf engine itself from 90 to 100 



Weight of inflamed cinders in a cavity presenting 



about 4 feet surface of tube • 25 



Supply of coal for one hour G 



Water for ditto, allowing steam of one atmosphere 



to be --gVtr the specific gravity of water • 32 



1G3 



This statement I do not propose this statement in any other light than 

 »erdy an ap- as a rnt | e approximation to truth, for as the steam is ope- 

 proxunation. . , r . "-"'.. , „ . . . 



rating under the disadvantage or atmospheric pressure, it 



must be raised to a higher temperature than in Messrs, 

 Eonlton and Watt's engine ; and this will require mo-e fuel ; 

 but if it take twice as much, still the engine would be suf- 

 ficiently light, for it would be exerting a force equal to 

 raising 550 lb. one foot high per second, which is equiva- 

 lent to the labour of six men, whereas the whole weight 

 does not much exceed that of one man. 

 Another ftrst It may seem superfluous to inquire farther relative to 

 jrcover faA movers for aerial navigation ; but lightuess is of so 



much value in this instance, that it is proper to notice the 

 probability that exists of using the expansion of air by the 

 sudden combustion of inflammable powders or fluids with 

 great advantage. The French have lately shown the great 

 power produced by igniting inflammable powders in close 

 vessels ; and several years ago an engine was made to work 

 j» this country MB a similar manner,' by the inflammation of 

 spirit of tar. I am not acquainted with the mane of the 

 person who invented and obtained a patent for this engine, 

 >)ut fmui some minutes with which I was favoured by Mr. 



Williara 



