TBANSACTIONS OF SECTION 0. 871 



than to increase of muscular stress. I have timed sea-gulla and found them to flap 

 their wings two hundred times per minute when flying at about 24 knots per 

 hour, and haye estimated eider-ducks, making about 3G knots per hour, to be 

 flapping their wings five hundred times in a minute. I say ' estimated,' for their 

 movements are too rapid for precise counting. This outpouring of energy, which 

 seems to me to be unequalled in terrestrial animals, is nevertheless maintained by 

 birds for indefinitely long periods of time. 



A proportionately increased rate of combustion and renovation of tissue as well 

 as of food-consumption are necessary consequences. The higher temperature of 

 the bodies of birds, as compared with other animals,' and the well-known voracity 

 of those which, like sea-birds, are almost continuously on the wing, are circum- 

 stances which seem to point to the same conclusion. It is confirmed by what we 

 know of steam and other motors. For instance, if a steamship were so built and 

 proportioned that a ton of coal per hour consumed in the boilers would maintain the 

 pressure at 100 lb. per square inch and produce 1,000 horse-power at the propeller; 

 and then if, without other alteration, tiring was slackened until the steam fell to 

 50 lb. per square inch, and there maintained, it is clear that the horse-power pro- 

 duced would be greatly lessened, and so would the temperature of the steam in 

 the boilers, steam-pipes, and cylinders. Thus, other things being equal, the tem- 

 perature of the steam would rise and fall with the energy given forth by the 

 mechanism. 



The suggestion is that the higher temperature of birds, as compared with other 

 animals, is similarly connected with their superior power of producing and main- 



taining energetic efibrt. 



AERIAL NAVIGATION. 



Let us now consider what man has done, and may be able to do, in aerial 

 navigation by aid of contrivances which, as in the case of railway locomotives and 

 ocean steamers, are propelled by a power other than that of his own body. 



The scientific world is greatly indebted to Mr. Hiram S. Maxim, of London, for 

 recording in a clear and readable form the present position of aeronautic mechanisms,-* 

 So far, the only contrivances which have been fairly successful are balloons, which, 

 unlike birds, depend on atmospheric displacement for their power of sustaining 

 weight or rising or falling. 



In balloon experiments our French neighbours have led the way, from the 

 first attempt of the Montgolfier brothers in 1783. During the last twenty years 

 they have made numerous experiments and substantial improvements. Captain 

 Henard and other officers of the French Army have constructed a fish-shaped 

 apparatus, and inflated it with hydrogen. It is driven by an electric motor of 

 8i horse-power, and has sufficient buoyancy to carry two aeronauts and all neces- 

 «ary accessories. In fair weather Captain Renard has succeeded in travelling at 

 the rate of 12| miles per hour, in steering in any direction, and even in returning 

 to his point of departure. The balloon, it is said, always keeps level, and so far 

 there have not been any accidents ; but no expedition has been attempted in wet 

 or windy weather. 



Except that a more powerful motor, going at a higher speed, might be fitted 

 to such an apparatus, Mr. Maxim thinks that it is as near perfection as is ever likely 

 to be reached by a machine depending on aerial flotation. He proceeds to give an 

 account of some experiments made by Professor S. P. Langley, of the Smithsonian 

 Institute, Washington, and of others by himself, to ascertain how much power is 

 required to produce artificial flight by means of aero-planes, after the manner of 

 tirds, and whether such power can be obtained without exceeding the weight which 

 it would itself sustain. 



' Chambers's Enci/clopcedia, ' Bird ' and ' Animal Heat' ; Zehrhich der Zoologie, by 

 Professor Hertwig, p. 5.38. 



^ ' Progress in Aerial Navigation,' by Hiram S. Maxim, Fortnightly B^vi-ew, 

 October, 1892. 



