116 CS. Peirce—On a Method of swinging Pendulums. 
dulums was not over four seconds a day, a elgg attainable 
adjustment. Then the period would reduce : 
mex eh ed. 
g 
The terms x—y here indicate that the apparatus would still 
‘be subject to a correction for flexure: but it would be only for 
the relative flexure due to the distortion of the support between 
the two knife-edges. This could of course be made very small. 
It would still have to be measured: but it would be measured 
once for all, since it would be the same at all stations. At 
present, the measurement of the flexure at each station, involv- 
ing as it does the erection of a separate pier, threatens to be 
one of the most troublesome and expensive parts of the whole 
work of determining gravity. This would be entirely obviated 
aye's plan, except that the small differential flexibility 
would have to be determined once for all. The e proper way to 
make the stand so as to bind the two knives to their relative 
position as firmly as possible while allowing a moderately large 
flexibility to the whole stand, so that the two pendulums could 
freely influence one another, ‘would easily be found out. 
2. 
ANIA Pa 
q aA taalaia’ 
The average period of oscillation iN oe pendulum, after 
correction for spree wold be that —— to a simple 
pendulum having the length /, a mean of e 
two simple pendulums whose natural periods of oscillation 
would be the same as those of t the given pendulums. But 
a this would be the average time of oscillation of either 
um, serie neither pendulum would have all its oscillations 
It is, therefore, necessary to inquire 
whee error Soria arise owing to the observations not extending 
over any exact number of cycles of motion, so that the mean 
