DowLiNG AND DoNNELLY — Measurement of Short Time Intervals. 169' 



Each wire was stretched between two spring clips {aa, fig. 2), about 3 cms. 

 apart, mounted on a rectangular piece of thin ebonite (h). Midway between 

 the clips a large hole was pierced in the ebonite. On either side of this hob- 

 lay two stout copper wires fixed to the ebonite, and across them the fine 

 wire {d) was stretched, and pressed lightly on them at the points of contact. 

 One of these was then clamped over the other, so that the wires (d) were 

 at right angles, small-distance pieces of ebonite being interposed, and the 

 distance between the wires [d, d) was measured by a microscope with a 

 vertical micrometer motion. The arrangement was then carefully mounted 



a 



Fig. 2. 



so that both wires {d) were in the line of fire, and connexions made from the 

 support wires (c, c) to the electrical apparatus. On either block one of the 

 wires (c) corresponded to ^ or 5 respectively, while the other one of course 

 took the place of D in the original arrangement. One difficulty was found, 

 but was easily met. Owing to the resistance introduced at the points of con- 

 tact (c, d), there is a noticeable drop in potential across the gap {AD). 

 This had to be balanced across the condenser, and a potential-dividing 

 arrangement PQr was substituted for the former direct-earth connexion 

 shown at (fig. 1). With this refinement, some few observations were made 

 which indicated that measurements of intervals of about 40 micro-seconds 



SCIENT. PROC. R.D.S., VOL. XVI, NO. XV. 2 B 



