254 



REPOR'J 



-1875. 



scale of the spring, and cousequently the natural period of oscillation of the weight, 

 can be varied at will. When it is so adjusted that it sjoichronizes with the waves, 

 the oscillations become very violent, and a large amount of power can be obtained 

 from them. The theoretical amount of power per minute in foot-lbs. obtainable, 

 when the synchronism is perfect, is equal to 57-7 X the range of oscillation of the 

 weight X the mass of the weight in lbs. X the etfective height of the waves in feet, 

 divided by the cube of the period in seconds. 



»«=mas3 of oscillating weight, in lbs. 



P = period of oscillation, in seconds. 



x= range of vertical oscillation of ship, in feet. 



y = range of vertical oscillation of weight. 



Maximum force on spring =F = - 



P'ff 



Work per oscillation in foot-lbs. = the area of ollipse=w = 



Work per minute = 





p3 • 



F.V7 



~2' 



ir'ynix 



The manner in which this result is arrived at is explained by the diagram. Tlie 

 dotted wavy line represents the motion of the ship through one oscillation, and the 

 full wavy line that of the weight. The distances between these two lines are indi- 

 cated by the ordinates a, b, c, d, &c., which also represent the tension of the spring. 

 Whenthe ship is rising the spring is pushing down, and when it is falling the spring 

 is pulling up, thereby affording a resistance against which the ship can work. The 

 ordinates «, b, c, &c., planted as oi-dinates on a line which represents the vertical 

 motion of the ship, make an elliptical figure, the area of which represents the work 

 taken out of the ship and put into the oscillating weight in one complete oscillation. 



In practice the spring would consist of highly compressed air pressing on the rams 

 of hydropneumatic cylinders ; and the arrangement is such that the vessel containing 

 the compressed air forms the moving weight. The natm-al period of oscillation in 



seconds =27r 



V 



"9 



, in which c is the capacity of the air-vessel in cubic feet, and 



a is the sum of the area of the rams in square feet. 



The author exhibited a design for a machine for working an auxiliary propeller 

 of a sailing-ship of 1800 tons displacement. The moving weight in this case is 

 200 tons ; and ho showed by calculation that with a range of oscillation of 20 feet 

 it would give, after allowing for friction, about 30 horse-power in the long swell 

 met with in the tropical calm, 2()0 horse-power in average ocean-waves, and more 

 than 600 horse-power in a heavy head sea. The space occupied by the machine 

 compares favourably with a steam-engine of the same power. 



The author exhibited a model of the machine, which in a moderate sea had yielded 

 power at the rate of 1 J horse-power per ton of moving weight. 



On a Revolution-Indicator. Bt/ Beauchamp Towbk. 



The simplest form of the instrument invented by the author is a centrifugal 

 pump. The centre of the pump-case is connected to a small tank, and the periphery 



