Manchester Memoirs, Vol. xlvi. (1901), No. 5. 5 



explosion, the piston P will be forced outwards a certain 

 small amount corresponding with the elastic compression 

 of the material of which the spring is made. This motion 

 is transmitted to the exterior by the rod R. 



The lever Z, supporting the mirror, rests on the 

 fulcrum /^ at " 3 " ; it is kept against the knife edge " 2 " 

 of R by the tension of the wire W. The wire VV is of 

 considerable length, and is stretched to near its limit of 

 elasticity. The lever L can, therefore, follow the small 

 advance of the rod R without greatly diminishing the 

 tension of the wire W. 



The mirror focuses a point source of light on to a 

 rapidly revolving cylinder, thus recording on a magnified 

 .scale the motion of the piston P. It is not impossible 

 that an indicator of this type would work in practice, but 

 the deflection of the mirror, and therefore the scale of the 

 records obtained would be much too small. To increase 

 the deflections three modifications are necessary — the 

 spring .^ must be made longer, the ratio of its cross- 

 sectional area to that of the piston be decreased, and the 

 knife edges " 2 " and " 3 " be brought closer together. 



In Fig. 2 the design of the actual instrument is given, 

 the lettering being the same as in the previous figure. 



j3. 



Fig. 2. 



Section of Recording Manometer for High-Pressure Explosions. 



By means of the thread U, the gauge screws into the 

 explosion chamber, C being flush with the inside surface. 



