NEWTONIAN CONSTANT OF GRAVITATION. 55 
and if the times of transit are corrected by one quarter of their second ditierence, so 
as to approximate to the times of transit of the point of rest, the half period over the 
whole series becomes 
96°645 seconds. 
The object of examining so many transits is not so much with the idea of applying 
methods of least squares or of otherwise equalising errors, but mainly to see that the 
oscillation is going on regularly and that no sudden disturbance has arisen which, if 
it were undetected at the time, might become lost and yet leave the result in error 
by an observable amount. I find that in the present instance I did not try to improve 
upon the obseryations by arithmetical manipulation, and that 96°650 was taken as 
the observed half-period. Two small quantities had to be subtracted from this, one a 
correction of — ‘0034 due to a gaining rate of two seconds a day of the clock, and one 
of — ‘1508 on account of the damping effect of atmospheric resistance. The true 
whole period for no damping then becomes 192:992 seconds, and its square 37245°9 is 
the quantity which is finally made use of in the dynamical calculation. It is recorded 
as T;”, the square of the time with the balls on. In a similar manner T,” is found 
when the counterweight is on, and To” when the mirror alone is swinging. 
Under this heading the deflections produced in Operations 11, 12, 13 must be con- 
sidered. The deflection in Operation 10 is due to four possible attractions :-— 
(1.) Lead balls, &e., on gold balls. 
(2.) Lid and permanent fixtures, &c., on gold balls. 
(3.) Lead balls, &c., on beam mirror. 
(4.) Lid and permanent fixtures, &c., on beam mirror. 
The deflection, if any, of Operation 11, is due to (3) and (4) above. Similarly the 
deflection produced by Operation 12 is due to (4) alone, and of Operation 13 to (2) 
and (4). Knowing, therefore (1) + (2) + (3) + (4); (3) + (4); (4); and (2) + (4); 
(1), (2), (3) and (4) are separately determined. ; 
I have on two occasions since Experiment 3 was completed (which was of a semi- 
provisional nature) carried out the deflection observations of Operation 11. On 
September 1, 1893, 1°5 units or ‘15 division was obtained. There was a very slight 
+ creep. On September 11, with no creep and very consistent behaviour, °5 unit or 
‘05 division was obtained, Ido not know whether I should take ‘5 or 1 unit. The 
difference is beyond what can be observed with any certainty. 
I find that the lid was turned 180° between the two experiments, but this could not 
make any difference. I have taken 1 unit as the deflection in Experiments 4 to 12, 
and have calculated what it should be in Experiment 3. 
Most careful observations on September 2 and 3, 1893, fuiled to show any deflec- 
