vm. FORCE. 83 



41 5 a. Revolution Indicator, to show the rate at which 

 machinery is working. Frederick Guthrie, F.R.S. 



From the machinery an up-and-down motion is communicated to a piston 

 of a pneumatic forcing pump. The compressed air escapes through a fine 

 opening, and also exercises pressure on oil, water, or mercury, in a vessel 

 provided with a manometer tube. The height of the liquid in the tube 

 measures the rate at which the pump and machinery are working. 



VII. MEASUREMENT OF MOMENTUM. 



417. Model of the Ballistic Pendulum, erected in the 

 Royal Arsenal in 1814, and transferred to the Royal Military 

 Repository in 1836. Weight, 7,740 Ibs. Centre of gravity below 

 centre of suspension 10'97 ft.; centre of oscillation below centre 

 of suspension 1 1 88 ft. Scale Jth. Major M. L. Taylor, R.A. 



418. Navy Electro-Ballistic Apparatus. 



Major M. L. Taylor, R.A. 



419. Model of Ballistic and Gun Pendulum, as erected 

 at Shoeburyness in 1858. Oscillating system of gun pendulum, 

 weighs 37 Ibs. 10-5 oz. ; that of the block pendulum weighs 

 31 Ibs. 8-25 oz. Scale, th. Major M. L. Taylor, R.A. 



41 9a. Spring Balance, with arrangement for suspending the 

 lever and the scales on steel springs. 



Physical Institute of the University of Halle (Prof. 

 Knoblauch, Director}. 



VIII. MEASUREMENT OF FORCE, 



42O. Cement Testing Apparatus, for ascertaining the 

 tearing strain of Portland and other cements, in sections of 11 

 square inches. Originally designed for the Metropolitan Board 

 of Works. Press for removing bricks from mould ; and Moulds 

 for making test bricks. Patrick Adie. 



42Oa. Michele's Patent Cement Testing Machine. 



De Michele, Rochester. 



The block to be tested is placed in the jaws prepared to receive it, the handle 

 is then turned, which raises the weighted lever by exerting- a pull on its short 

 end through the medium of the cement block. When the leverage is so in- 

 creased as to exert a force too great for the cement to sustain, it breaks, and 

 the lever falls, leaving the main-pointer at the spot to which it had been 

 raised. The arc along which the pointer moves is graduated to show the 

 number of pounds of tensile strain applied. A suitable arrangement, when 



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