﻿Ignition of Gases by Sudden Compression. 89 



overrunning the -lamp in this way was to make it flicker 

 brightly, so that when the indicator mirror was rotated by 

 the dropping weight, the reflected light made a horizontal 

 line of dashes across the photographic plate, the interval 

 between the middle of two consecutive dashes corresponding 

 to the interval between two contacts on the uniformly 

 rotating disk. The magnitude and uniformity of the velocity 

 of rotation of the indicator mirror by the falling weight 

 could thus be measured. Records were taken with falling- 

 weights of 8, 24, and 40 lb. 



To show the uniformity of motion during descent, the 

 results of measuring two plates taken with the 24-lb. load 

 are given in full. The apparent variations in any single 

 experiment are due rather to the difficulty of estimating the 

 centre of a flicker to 0*1 mm. than to any real variation in 

 the rate of fall of the loaded piston. 



Plate B. 



0-65 cm. 

 1-30 

 1-95 

 2-6 



3-28 

 395 

 4-58 

 5-22 

 585 

 651 

 7-12 

 7-78 

 8--10 

 9-06 

 9-70 



Mean 1 flicker in 0132 cm. Mean 1 in 0*129 cm/ 



1 flicker = •0304 second. 

 . * . 1 second = 4*34 cm. on plate. 1 second — 4*26 cm. 



Mean 4'30 cm. = 1 second. 



Similar records with loads of 8 and 40 lb. gave time 

 scales of 



2*22 cm. = 1 second 

 and 5*77 cm. = 1 second. 



The means for the two plates with 40-lb. load were 5*75 and 

 5*79 cm. per second, so that it may safely be assumed that 

 the time scale was known correctly to within 2 per cent., and 

 probably less. This is a degree of accuracy as great as 

 that with which,, as a rule, it is possible to measure the 

 records. 



The vertical movement of the weights was about 7 inches, 





Plate A. 



5 flickers in 0*70 



10 



1-34 



15 



2-0 



20 



266 



25 



330 



30 



3'98 



35 



463 



40 



529 



45 



5-93 



50 



659 



55 



7-22 



60 



7-90 



65 



8-53 



70 



9-21 



75 



9-89 



