1900.] 



on Recent Studies in Gravitation. 



281 



experiment gives the mass of the earth in terms of that of the big 

 sphere, and so its mean density. This experiment has often been 

 repeated, but I do not think it is too much to say that no advance 

 was made in exactness till we come to quite recent work. 



By far the most remarkable recent study in gravitation is 

 Professor Boys' beautiful form of the Cavendish experiment, a 



Fig. 2. — Boys' Apparatus. 



research which stands out as a model in beauty of design and in 

 exactness of execution (Fig. 2). But as Professor Boys has described 

 his experiment already in this theatre * it is not necessary for me to 

 more than refer to it. It is enough to say that he made the great 

 discovery, obvious perhaps when made, that the sensitiveness of the 

 apparatus is increased by reducing its dimensions. He therefore 



* Proc. R.I. xiv. part ii. 1894, p. 353. 

 Vol. XVI. (No. 94.) u 



