33S 



SCIENCE 



[N. S. Vol. XXXVI. No. 924 



but we describe 'them differently. Calorie 

 has a physical existence, instead of being 

 merely the logarithm of the probability of 

 a complexion. In common with many ex- 

 perimentalists, I can not help feeling that 

 we have everything to gain by attaching a 

 material conception to a quantity of caloric 

 as the natural measure of a quantity of 

 heat as opposed to a quantity of heat en- 

 ergy. In the time at my disposal I could 

 not pretend to offer you more than a sug- 

 gestion of a sketch, an apology for the pos- 

 sibility of an explanation, but I hope I may 

 have succeeded in conveying the impression 

 that a caloric theory of heat is not so en- 

 tirely unreasonable in the light of recent 

 experiment as we are sometimes led to 

 imagine. H. L. Callendar 



THE PMOBLMM OF MECHANICAL FLIGHT 

 HISTORICAL resume; 



The scientific period in aviation began in 

 1809 when Sir George Cayley published in 

 Nicholson's Journal the first complete me- 

 chanical theory of the aeroplane, in which he 

 put clearly in evidence the fundamental prin- 

 ciple of sustention obtained by velocity. This 

 memoir passed unnoticed until unearthed 

 some sixty years later by Penaud. Following 

 Cayley there was a long unfruitful interval 

 in which fell the projected aeroplane of Hen- 

 son in 1842-43, the attempts at gliding by 

 Le Bris in 1856, and the biplane gliders of 

 Wenham in 1866. At the end of the Franco- 

 Prussian war interest in heavier-than-air fly- 

 ing machines was revived, and the Soeiete 

 frangaise de Navigation aerienne was from 

 1872 on composed of a number of investiga- 

 tors engaged in the conquest of the air. The 

 history of their endeavors is found in " L' Aero- 

 nauts." Among them was Alphonse Penaud, 

 a young mechanic whose early death prevented 

 him from pushing his researches to their log- 

 ical end. Penaud was less isolated than 

 Cayley and one of his memoirs was crowned 

 by the Academic des Sciences. He constructed 

 the first toy aeroplane, with the propeller in 



the rear and driven by a rubber band. This 

 apparatus flew for an appreciable time, utiliz- 

 ing motive energy which it carried with it, 

 and this property differentiates very sharply 

 the experiment of Penaud from those of his 

 predecessors, in which was realized only a fall 

 more or less retarded by the air. 



The German Lilienthal followed Penaud, 

 and from 1891 studied the equilibrium, ma- 

 neuvering and landing of gliders, falling to 

 his death on his two thousandth flight, Au- 

 gust 9, 1896. In this country the French 

 engineer Chanute and the American Lang- 

 ley had meanwhile been experimenting and 

 developing the laws of aerodynamics, Lang- 

 ley's work going as far back as 1887 and con- 

 tinuing until his unsuccessful attempts at 

 flight in 1903. In 1891 he published' the 

 results of his researches, and definitely stated 

 that it was possible to construct machines 

 which would give such velocity to inclined 

 surfaces that bodies indefinitely heavier than 

 air could be sustained upon it and moved 

 through it with great speed. 



By the end of the nineteenth century ef- 

 forts to build aeroplanes had become numer- 

 ous. Sir Hiram Maxim in England and 

 Ader in France both constructed machines 

 and made attempts to fly them. Maxim built 

 in 1890-95 a flying machine with 557 square 

 meters of surface and 3,640 kilograms weight, 

 which was damaged before leaving the ground 

 and abandoned. The " Avion " of Ader was 

 tested on the field of Satory in 1897 before the 

 rspresentatives of the French War Depart- 

 ment, but its performance led the department 

 to withdraw its support and experiments 

 were discontinued. Langley as early as 1896 

 had designed and built a small steam-driven 

 model aerodrome weighing about 13 kilo- 

 grams, and on May 6 of that year he flew it 

 some 1,200 meters over the waters of the Po- 

 tomac. The quarter-size model of his large 

 man-carrying aerodrome flew successfully 

 about 1,000 feet near Widewater, Va., on Au- 

 gust 8, 1903, but the large machine itself, 

 carrying Mr. Manly, was injured in launching 



^ ' ' Experiments in Aerodynamics, ' ' Smithsonian 

 Contributions to Knowledge, Vol. 27, 1891. 



