58 
PUTNAM. 
P 
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a set of quarter second pendulums, with receiver and flash 
apparatus correspondingly reduced in size. In general 
principles these are similar to the half 
second apparatus, although there was 
added an ingenious device, designed 
by Mr. Fischer, for starting and stop¬ 
ping the pendulum, and the flash apparatus 
is somewhat different. The pendulum re¬ 
ceiver is about 5 inches by 6 inches (13 cen¬ 
timeters by 15 centimeters) and 7 inches (17 
centimeters) high, and may be exhausted with the 
portable air pump to 1.5 inches (40 millimeters) in 
half a minute. The pendulums weigh about 0.7 
pound (300 grammes) each. The entire apparatus, 
with its packing cases, weighs about 106 pounds 
(48 kilograms), and is undoubtedly the smallest 
and most compact ever used for the purpose. The 
relative sizes of three types of pendulums are 
shown on Fig. 3, P being the Peirce reversible 
meter pendulum, A the half second, and C the 
quarter second, all drawn to the same scale. 
To test the efficiency of this apparatus, as well as 
the agreement of results with pendulums of differ¬ 
ent lengths, these pendulums were swung simul¬ 
taneously with the half second pendulums at three 
1 , of the stations of the transcontinental series, as 
well as at Washington, before and after this work. 
_L To increase the value of the test, the stations se¬ 
lected, Chicago, Denver, and Pikes Peak, were such 
as to give a maximum range of conditions as 
respects magnitude of g and difference of tempera¬ 
ture. The method adopted in using the apparatus 
was to swing each of the three pendulums, Cl, 
C2, and C3, once in each position, with an 
air pressure of 40 millimeters, initial total 
arc about 1° 20', and length of swing 4 
hours. Both sets of apparatus were always set up in the 
rs 
Fig. 3.—Pendulums, 
natural scale. 
