108 Zrowbridge and Duane— Velocity of Electric Waves. 
them, and only occasionally do sparks occur that indicate more 
than five or six good complete oscillations. Hence these first 
few oscillations have the preponderating influence in fixing the 
length of the waves as indicated by the bolometer. In examin- 
ing the sparks, therefore, we measured from the first oscilla- 
tion as far down the spark as we could without passing over a 
space where dots were obliterated, and hence in every case we 
knew the number of dots between the points from which 
measurements were taken, and did not have to assume that 
good oscillations had occurred without affecting the plate. 
The following table, containing the results of our measure- 
ments with the improved apparatus, explains itself. The dis- 
tance from the mirror to the photographic plate was 302™ in 
each ease. 
No. of Distance be- Time Length Velocity 
revolutions tween succes- of of of 
of mirror Sive points on oscillation wave waves 
per sec. plate in cm. sec. em. em. 
70°8 "05028 1°869 x 10" 5670 3°030. 1a. 
fou 05247 1°877 X10" 5670 302r 16" 
ioe 05536 1°940 x 10’ 5670 2 O23" Or 
69°5 "05002 1°897 X10" £690 3°000  Xro” 
68°9 ‘04900 1°876 X10" 5690 3°084 «10 
69:0 04974 1°899 x 107 5690 2:996 x10" 
To 05075 1°879 x 10" 5660 3013506 Oe 
Average value of velocity, 3°0024 x 10” 
With the exception of three preliminary trials, which gave 
values differing from the mean by 10 or 12 per cent, these are 
the only complete determinations we have made. 
In some cases the waves in the circuit were just as good 
with the spark gap as without. In others there was a decided 
wave formation when sparks occurred, but the node was not 
quite so well marked. For this reason, and since it did not 
appear to make any difference in their length, the waves 
usually were measured without the spark gap. As the sparks 
were quite regular, the difference in the bolometer readings 
must have been due to Faraday tubes, that were reflected from 
the spark gap, without forming a spark and reversing them- 
selves. 
As an example of the data taken to ascertain the position of 
the node we give the following table. The top line contains 
the distances of the bolometer terminals from arbitrary fixed 
points on the cireuit. 
Distances from fixed points, 2008 40°™ 6o°™ 
4°3 4°0 4°3 
Bolometer deflections, 4°5 4°] 4°4 
4°5 4 4°2 
Average deflections, 4°43 4°03 4°3 
