62 PROFESSOR C. V. BOYS ON THE 
centimetre®/gramme second’ units it is merely necessary to multiply by 16°3861, the 
number of cubic centimetres in a cubic inch. 
To obtain from this the density of the earth I might have recalculated the 
attraction of the earth treated as a rotating ellipsoid composed of similar shells of 
equal density as given in Professor Poyntine’s paper, but since it is obvious that 
G A is a constant, and is, taking Poyntrne’s figures, equal to 36°7970 X 107%, it is 
merely necessary to divide this figure by G to find A. 
Again, taking Experiment 8 to furnish an example, these operations are as follows :— 
: PS 3695-4" x °00119598T 
= —__ = = 2 =o 
~ 4QD 4 x 1942882 x 139965 UEDA Xs 

in inch?/gramme second” units. 
Multiply by 16°3861, then G = 6°6579 x 10-% in C.GS. units, and A = 5°5268. 
The more important quantities of the whole series of experiments are exhibited in 
Table I, which, as the heading shows, is constructed on the Inch, Gramme, Second 
system, in conformity with the actual measurements. The supplementary table is a 
repetition of the most important quantities in C.G.S. units. Here below the constant 
of gravitation G is to be found the series of values of A the mean density of the 
earth. Appended are Cornv’s and Poyntno’s values, Cornv’s G being obtained from 
his A in the same way that I obtained my A from my G. 
An examination of the table shows that I have employed a fair variety of con- 
ditions, the lead balls alone being unchanged throughout the series. Three pairs of 
small masses were made use of. The lead balls were practically unchanged in 
distance, though, after Experiment 7, they were brought nearer together by 39 inch 
about. The effect of this on the deflection P and the coupie Q is at once evident in 
Experiment 8. Three fibres were employed, though, as already mentioned, the 
rigidity was very different in Experiment 9 owing to the great longitudinal strain. 
The different torsional rigidities are tabulated under S. 
The periods are tabulated under their squares, 7.¢., after correction for damping. 
T,? is with the gold balls or cylinder suspended from the mirror and with the lead 
balls at a + or — position, where, by producing a maximum couple, they do not 
affect the period. Ty? is the corresponding period with the lead balls in their neutral 
position where they accelerate the period. I might, following Reicu, have inde- 
pendently calculated G from the acceleration produced in this way, but these periods 
were not determined with the same care as the others, and in any case, the difference 
is too small for an equally accurate result to have been obtained. T,? and T,” are the 
square of the periods with counterweights and with nothing on the mirror. 
The pairs of quantities tabulated under H,™ and h," are the four differences of 
levels between the lead and gold balls. Thus 60296 in Experiment 5 is the 
* 36954 = 36964 —1. See p. 56. 
+ 00119598 = :00119615 (1 — 1/7850). See p. 35. 
