MECHANICS AND USEFUL ARTS. 59 



would be created. This evil would be remedied, though not 

 without sacrifice of lightness, if a stock of petroleum were carried 

 instead of a receptacle of gas, and tlie vapor of petroleum used 

 instead of gas for explosion, with a due admixture of atmospheric 

 air. Another source of motive power is afforded by solid explo- 

 sive substances, i. e., by comjiounds which on combustion gener- 

 ate a large volume of gaseous products. Such are gunpovv'der, 

 gun-cotton, the mixture used for rockets, etc. In case of an en- 

 gine worked by such power, the weight of boiler, fuel, and water 

 necessary to the steam-engine is replaced by that of the suj^ply 

 of explosive material, whereby for short journeys a great reduc- 

 tion in weight is ett'ected. There are some further considerations 

 which seem to show that these powers are capable of achieving, 

 to some extent, the desired result, which the steam-engine, prob- 

 ably with justice, is pronounced incapable of eft'ecting. If a very 

 diminutive steam-engine could be made capable of raising itself 

 into the air, a powerful steam-engine could be made to do so 

 likewise ; for the ratio of weight to power is greater when the 

 steam-engine is small than when it is large ; and this holds good 

 in the case of most machines or engines. Now, rockets are actu- 

 ally made capable of lifting themselves into the air, and if small 

 rockets can do this, surely, in accordance with the above princi- 

 ple, large rockets can do so too, and in proportion to the size of 

 the rocket, its power of lifting a load will increase ; and if this be 

 so, it must be possible to construct a rocket, or a combination of 

 rockets, capable of lifting from the ground and transjiorting to 

 some distance the weight of a man. The weight actually lifted 

 by the larger Congreve rockets is not inconsiderable ; but it is 

 proper to consider that this would be greater were the power of 

 the gas brought differently into play. For the rising gas acts 

 much more advantageously when the rocket is movins: at a his'h 

 velocity than when it is stationary, — a large projiortion of its 

 power being Avasted in the latter case. Could the j)ower act as 

 advantageously when the rocket is stationary as when it is 

 moving at full speed, it would be caj^ablc of lifting from the 

 ground a greater weight than it actually does ; and a greater 

 suj^ply of material being lifted, an increased range of flight could 

 be obtained. For this reason, a rocket, however great its power, 

 would be wholly unsuited to the purpose of aerial navigation ; it 

 being impossible to retard its speed without diminishing the 

 power exerted by it. But no such objection exists if we conceive 

 the gas to produce motion, not directly, but by means of a pro- 

 peller. For the propeller may revolve at full velocity, and thus 

 the maximum of availaljle power be brought into play, Avhile the 

 engine itself is moving through the air slowly or not at all. The 

 same reasoning holds in reference to the Chinese turbines — i. e., 

 that the ratio of weight to power would l)e greater Avhen they are 

 small than when they are large. And in this case, if a small tur- 

 bine can lift itself into the air, a fortiori, a large one can do so. 

 Such considerations seem to show that, though the steam-engine 

 may be wholly incapable of accomplishing the feat in question, 

 yet that other powers now known to us are capable of effecting 



