426 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
dirigible balloons, stating, that the highest speed yet reported 
is 23 miles per hour. The gliding machines, as LilienthaFs, 
were spoken of. Coming to power-driven machines, heavier than 
the air, it was stated that models were flown in 1842 and 1878, 
and that in 1868 Stringfellow built an apparatus with engine 
and boiler, using the superposed planes suggested by Wenham. 
About 1891 Langley and Maxim published the results of experi¬ 
ments on the principles underlying such apparatus. Some de¬ 
tails were given of Mr. Langley’s aerodrome, and of the acci¬ 
dents in launching it last Fall. Its 52 horse-power gasoline 
motor weighs only 200 pounds, with cooling water and all acces¬ 
sories, or 2.2 pounds per horse-power for the engine alone. [Not 
published.] 
In the discussion that followed, Mr. Langley emphasized the 
value of Mr. Zalim's experiments, of Mr. Manley's work in re¬ 
ducing the weight of the motor, Mid Professor Bell's novel sup¬ 
porting planes. Mr. Bell told of the curious history of the idea 
of “air-ships,” and said Mr. Manley was the first person to risk 
his life on a power-driven aeroplane. Mr. Bigelow spoke of 
witnessing some experiments with Bell's tetrahedral kites during 
the past summer. Mr. Thompson gave a summary of some re¬ 
cent theoretical work on the stability of aeroplanes, and Mr. 
Whittlesey spoke of the 300 patents for aerial navigation, and 
of the refusal of the Patent Office to recognize any device without 
a gas-bag as operative. 
582d Meeting. March 12, 1904. 
President Marvin in the chair. 
Twenty-seven persons present. 
Mr. A. F. Zahm concluded his paper begun at the last meet¬ 
ing, presenting several equations and discussing several problems 
arising in practice in aerodynamics. 
This paper and the general subject were discussed by Messrs. 
Manley, Marvin, and Fessenden. 
Mr. G. K. Gilbert then spoke on The feasibility of measuring 
tides and currents at sea,—a problem which appeals to the geolo- 
