158 POPULAR LECTURES AND ADDRESSES. 



cacy and consistency and accuracy to indicate 

 these results. 



A most earnest and persevering effort has been 

 made by Mr. George Darwin and Mr. Horace 

 Darwin to detect variations in gravity due to lunar 

 disturbance, and they have made apparatus which 

 notwithstanding the prodigious smallness of the 

 effect to be observed, is in point of delicacy and 

 consistency capable of showing it ; but when they 

 had got their delicate pendulum their delicate 

 plummet about the length of an ordinary seconds' 

 pendulum and their delicate multiplying gear to 

 multiply the motion of its lower end by about a 

 million times, and to show the result on a scale 

 by the reflection of a ray of light, they found 

 the little image incessantly moving backward and 

 forward on the scale with no consistency or regu- 

 larity ; and they have come to the conclusion 

 that there are continual local variations of ap- 

 parent gravity taking place for which we know 

 no rule, and which are considerably greater than 

 the lunar disturbance for which they were seeking. 

 That which they found continual motions of the 



