92 PROFESSOR C. V. BOYS ON THE 
A represents the lid reading differing from 85:9, the neutral position, by the 
azimuth 65° of the lead balls. The actual time of the beginning of a set is next 
marked and then the temperature of a thermometer set up close to the apparatus. 
This is illuminated and read by the same means that are provided for reading the lid 
vernier. 
The first column of figures are observed elongations expressed in tenths of scale- 
divisions. The second column contains the scale corrections, in which are included 

+ postion 

2449 




2080 


- position 

both the calibration and the circular errors. The third column are the corrected 
elongations, the fourth the differences of these or amplitudes, the fifth the ratio of 
these or the decrements, in the sixth are the quotients of each amplitude by 1 + the 
following decrement. The last column contains the algebraical sums of the corre- 
sponding numbers in the third and sixth columns. They represent the points of 
rest during the course of the oscillation. Each series gives a mean point of rest of 
which a dozen or more may be obtained in one night. I prefer to arrange all the 
individual points of rest as well as the mean points in their proper places in a 
diagram, of which abscissee represent the hour and the ordinates the points of rest, 
but on a very large vertical scale. The one of these for the evening’s work chosen 
for illustration is shown in fig. D, from which it will be seen that a gap of 368 inches 
has been cut out to save room. ‘The series of mean points of rest are shown in the 
following table :— 
