282 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1912. 



This device has already received various applications, especially in 

 the working of the turrets of gunboats. An analogous device is found 

 ill the aviation motor of Salnison vv^hich was shown at the last Salon. 

 In this we also find an oblique plate with a shaft carrying cylinders 

 with their axes parallel to that of the shaft and of which the pistons, 

 by pressing against a plate, are obliged to take a motion of rotation. 

 But in this case, instead of using oil, the pressure is produced by the 

 explosion of a mixture of air and a volatile oil, as in all gas engines. 



In 1909 I stated the principle of certain devices, called torsiom- 

 eters, which, as their name indicates, measure the torque of the 

 shaft of a machine in order to calculate the work transmitted by 

 that shaft. The same purpose is accomplished by the use of various 

 dynamometers. The following are two recent inventions whose 

 principle is interesting: 



In the Farcot dynamometer the driving shaft is connected to the 

 shaft of the dynamometer by means of a ferrule, threaded on the 

 inside so that it can move parallel along the shaft whenever the two 

 shafts have different speeds. The force which tends to displace the 

 ferrule is proportional to the force transmitted from one shaft to the 

 other. A suitable pressure parallel to the shaft is applied to counter- 

 act this displacement and is easily measured by a suitable balance, 

 the scale of which is so graduated as to give by direct reading the 

 power on a basis of 1,000 turns per minute. If the speed has a dif- 

 ferent value this reading must be niultij)lied by the actual number 

 of revolutions and then divided by 1,000. 



The Walton dynamometer uses a simple device susceptible of a 

 similar movement parallel to the driving shaft. The displacement 

 is here used to compress the oil contained in a small box and by 

 measuring this pressure the power consumed in the transmission may 

 be determined. 



Ernoult proposes to increase the efficiency of springs in a verj'- 

 rational manner. He remarked that when coiled steel springs are 

 submitted to torsion, for springs of equal weight, those of hollow wire 

 worked better tlian those of solid wire. Accordingly he was led to 

 construct helical, tubular springs, which for equal strength are much 

 lighter than ordinaiy sprmgs of the same form. For sprmgs made of 

 superposed strips, he increased the resistance to bending by substi- 

 tuting for the material of rectangular section that which has a slight 

 transverse curvature. 



Capt. Largier has constructed an apparatus which he calls a ten- 

 siometer, made to indicate the tension of a piece of wire. The device 

 consists in causing a definite length of the wire, limited by two 

 bridges, to vibrate and then finds what the length L must be in order 

 that the vibration may have a certain definite pitch. From this 

 value, the weU-known formula for ^dbrating strings allows the calcu- 



