6 Petavel, HigJi-Pressiire Explosions. 



An air-tight joint is formed by the ring D pressing against 

 a flat ledge.* The end of the gauge from Z? to £ is a 

 good fit in the walls of the explosion chamber, and the 

 joint is thus protected from the direct effect of the 

 explosion. 



The spring S, about 5 inches in length, is tubular in 

 shape. To prevent any buckling, it is made to closely fit 

 the cylinder, in which it is contained, at two places, d and 

 ei. The spring is fixed at the outer end Z, being held in 

 place by the nut K ; at the inner end it is free, and sup- 

 ports the piston P. The ordinary U leather is replaced 

 by a leather washer, attached to the piston by the screw C 

 and to the fixed part of the gauge by the rim E. The 

 end of the piston projects about one-hundredth of an inch 

 above the rim H, and it can therefore move back without 

 straining the leather. 



The mirror (not visible in the figure) is carried by the 

 lever L. This lever is so designed that the knife edges 

 I, 2 and 3 (see Fig. i) are in the same plane, it being at 

 the same time possible to bring the knife edges 2 and 3 

 within one-hundredth of an inch of each other, should so 

 great an amplification be found necessary. Up to the 

 present, however, the distance has not been decreased 

 below one-sixteenth of an inch, the scale obtained with 

 this distance being found satisfactor}\ 



With regard to the chronograph, there is but little to 

 be said ; the films on which the deflections are photo- 

 graphically recorded are wound on a drum which is kept 

 in rapid rotation by an electric motor, the usual devices 

 being used to regulate and measure the speed. The drum 



* Note. — In the case of apparatus designed for gases under high pres- 

 sures, all joints should be made directly metal to metal, no packing being 

 used. A joint thus made, if properly designed, is and remains absolutely 

 air-tight. It can be made or broken in an instant, and as many times as 

 may be required. 



