Flying Machines. 375 



abstruse question, the flight of birds, and he has established 

 good reasons for supposing that there has been much exagge- 

 ration in the popular estimate of the force exerted in the 

 operation. We hope our readers will have recourse to the 

 publication we have named; but, as an incentive to consult it, 

 and for the benefit of those who are not likely to see it, we 

 shall proceed to give a condensed account of its contents. 

 Mr. Wenham tells us that a weight of 150 lbs. suspended from 

 a surface of the same number of square feet, will fall through 

 the air at the rate of 1300 feet per minute, the force expended 

 on the air being nearly six-horse power. Consequently, that 

 power would be required to keep the same weight and surface 

 suspended at a fixed altitude. A man can perform muscular 

 work equal to raising his own weight, say 150 lbs., twenty- two 

 feet per minute ; but at this low rate of speed he would require 

 to sustain him on the air a surface of 120,000 square feet, 

 making no allowance for weight beyond his body. Thus, 

 attempts to construct bird-like wings, by which a man could 

 raise himself perpendicularly, appear quite impracticable. 



A pelican, shot by Mr. Wenham, on the Nile, was found 

 to weigh 21 lbs., and its wings measured ten feet from 

 end to end. During their flight, pelicans make about seventy 

 wing strokes per minute, and when they float on the air, a few 

 strokes in each minute appear sufficient to sustain them, and 

 there is no symptom of powerful exertion. Mr. Wenham also 

 noticed that flocks of spoonbills, flying at about thirty 

 miles an hour, at less than fifteen inches above the Nile's 

 surface, did not create a sufficient commotion in the air to 

 ripple the surface of the water. Studying the behaviour of an 

 eagle impelled to activity by a charge of large shot rattling 

 amongst his feathers, he also noticed that he had to run at 

 least twenty yards before he could raise himself from the earth. 

 Many other observations of birds are highly important, and 

 enable us to form some conception of the way in which various 

 kinds of wings perform their work. 



Citing Smeaton, Mr. Wenham informs us, that if a plane 

 moves against the wind, or the wind against a plane, at 

 the rate of twenty-two feet per second, 1320 feet per miaute, 

 or fifteen miles an hour, a force of one lb. per square foot 

 is obtained. When a falling body, having a weight of one 

 lb. to each foot of resisting surface, reaches that velocity, 

 the atmospheric resistance balances its weight, and keeps 

 it from descending faster. A man and a parachute, weigh- 

 ing together 143 lbs., will not fall with a greater velocity 

 if the parachute is kept in position, and has an area of 143 

 square feet. A fall of eight feet brings a body to the earth 

 with the same velocity, which is not sufficient to destroy life or 



