508 Prof. R. Threlfall and Mr. J. F. Adair. On the 



and in individnal readings, this was often a tiresome matter; the 

 symmetry of the fork-line was sometimes disturbed by a super- 

 imposed small ripple of different period to that of the fork. This 

 ripple was due to the independent vibration of the style attached to 

 the fork. Of course, as it was small it had no effect on the whole 

 number of beats, but made the estimation of the fractions more diffi- 

 cult and less accurate than would otherwise have been the case. It 

 is not very difficult in practice, however, to estimate from a slightly 

 rippled wave the position of the true crest, and this was always our 

 object in making the measurements, as we hoped to be as likely to 

 make them too large as too small, and hence to get rid of them in a 

 number of observations. This uncertainty is, of course, entirely of 

 the second order, and, as a matter of fact, is negligible compared with 

 the irregularity observed, even if it is not — as we consider — entirely 

 eliminated through the number of the observations. 



Experiments to find whether the Time-constant of the Gauges depended 

 on the Energy transmitted. 



It is obviously impossible to reproduce the exact conditions of 

 explosive pressure in a laboratory, and hence the gauges Were tested 

 with respect to .their time of action by dealing blows of different 

 intensity to the india-rubber diaphragms. This was accomplished by 

 means of pendulums of constant lengths but of varying masses. The 

 arcs through which the pendulums moved were also varied within 

 wide limits. The method of testing was as follows : — The myograph 

 was so arranged that the firing key completed the circuit of the 

 electromagnet of a relay apparatus. The armature of the relay in 

 its position of rest completed the circuit of an electromagnet which 

 held the striking pendulum (by means of an iron armature) in a fixed 

 position. The result of the fall of the myograph pendulum was, 

 therefore, to release the pendulum suspended opposite the diaphragm 

 of the gauge. The first scriber was arranged in such a manner that 

 it was brought into action directly the bob of the pendulum touched 

 the rubber diaphragm. To this end, the diaphragm was temporarily 

 coated with a strip of tinfoil, so that the circuit of the first scriber 

 comprised battery, tinfoil, and testing pendulum. The second scriber 

 was in circuit with the contact portion of the gauge in the usual 

 manner. Consequently, on dropping the myograph pendulum, a 

 record of the usual character is obtained on the smoked plate ; the 

 first epoch is that of contact of ike testing pendulum and the tinfoil, 

 the second epoch is that of the completion of the registering contact. 

 The pendulums employed were of different kinds. One set of experi- 

 ments were made with a pendulum composed of a light brass rod, 

 on which bobs of different sizes and materials could be screwed. In 



