NEWTONIAN CONSTANT OF GRAVITATION. 69 
change of 3/5 inch in 2R was made in this experiment, the effect of which is at once 
evident both in P the deflection, and in Q the geometrical factor. 
In Experiment 9, the conditions were completely changed by the substitution of 
gold cylinders for gold balls. As already mentioned, the torsional rigidity of the 
fibre was altered 5 per cent. by the great tensile strain, yet with every quantity 
redetermined the only change in the result was about 1 part in 1500. The old 
conditions were realised again in Experiment 10, except that I had taken the fibre to 
London, re-soldered the broken ends and waited three months, but the result only 
differed from that of Experiment 8, by 1 part in 60,000. Perfect conditions were 
met with again, the mean deflections for the two nights, January 6 and January 7, 
being 3516°5 and 3516°3. The last experiment on January 21 was disturbed, and the 
points of rest varied several units in the course of the night. I was compelled, 
moreover, on leaving the apparatus at 17", to take off the gold balls, replace them 
by the counter-weights, and after about three hours’ sleep, to return again and 
take the counter-weight period. This was far too soon for the temperature to have 
settled after disturbance, and in addition to this cause of error, I had only 10 minutes 
in which to take the period, and had then to hurry off with the drum record still wet, 
in order to be in London where I had to lecture at noon. I cannot, therefore, look 
upon this experiment with the same confidence as Nos. 7 and 10, and so with the 
exception of Experiment 6, all those that give the lower value for A have something 
against them. Under these circumstances, I cannot do otherwise than look to 
Experiments 7, 8, 9, and 10 as being the most likely to give a true value. Moreover, 
as Nos. 8 and 10 were both made under most favourable yet very different conditions, 
their closely agreeing figures carry more weight than the other two. I therefore 
conclude that A = 55270 and G = 6°6576 X 10~*. The fifth figure in such case is, 
of course, a purely arithmetical phenomenon, but I do not think that the fourth 
figure can be more than 1, or at the outside 2 in error. 
I had hoped to have made a greater number of experiments under more widely 
differing conditions, but the strain which they entail is too severe, for not only have 
I had to give up holidays for the last three years, but to leave London on Saturdays 
and occasionally to sit up all Saturday and Sunday nights at the end of a week’s 
work. The conditions, therefore, are too difficult for such an extended series as I 
should like to make to be possible, and I must after one more effort, leave the problem 
to others who have leisure, and what is of far greater consequence, a quiet country 
place undisturbed by road and railway traffic, and who possess the knowledge and 
manipulative skill which the experiment requires. 
Conclusion. 
I think it might be useful, now that the autumn has passed and I have been unable 
to make a new series of observations, if I were to state my views a3 to any change of 
