538 SCIENCE PROGRESS. 



brought safely to rest on the ground at the termination of 

 the flight. The principal requisites are : — 



(i.) A sufficiently powerful and light motor. 



(ii.) Propellers, and aeroplanes of sufficient lifting 

 power. 



(iii.) Balance and stability. 



(iv.) Appliances for steering and controlling the 

 machine. 



(v.) Strength and rigidity. 



(vi.) Means of landing safely, 

 (i.) T/ie vwtor. — The difficulties of [light at the begin- 

 ning of the Queen's reign were entirely different to and far 

 more insuperable than those of to-day. Up till quite 

 recently no experiments on artificial flight could possibly 

 have led to any practical successes owing to the want of 

 light powerful engines or motors. The great advance made 

 in late years in this direction, and which may be expected 

 to be followed by further and greater advances in connec- 

 tion with autocars, has already entirely modified the condi- 

 tions of the problem, and will probably continue to modify 

 them still further in the future. 



The early experimenters had no motive power to depend 

 on beyond that of their own muscles, and we now know 

 that man does not possess sufficient power in proportion to 

 his weight to maintain himself in the air. He can start 

 from the top of a hill and sail downwards through the air 

 under gravity, and his rate of descent furnishes a simple if 

 not quite accurate test of the power he would have to exert 

 in order to fly. For if, instead of sailing in a downward 

 path, a man wanted to fly horizontally, he ivould require to 

 exert about as muck horse-pozver as would enable Jiiui to I'un 

 up the hill cany lug the fiying machine with him, in the time 

 that the flying niachine takes to descend to the bottom. 

 Now Mr. Pilcher finds his rate of descent to be about 

 five feet per second under favourable circumstances, and 

 hence it follows that a two horse-power engine would be 

 necessary to keep him afloat. 



In discussing this point further, I cannot do better than 

 quote from the data collected by Mr. Jeremiah Head in his 



