384 POPULAR LECTURES AND ADDRESSES. 



sensibly from what it is when the chronometer is 

 laid on a hard board, the instrument being of 

 course always kept on its gimbals in its heavy 

 outer case. If, however, the cushion is soft enough, 

 the critical condition explained above may be 

 reached or even passed ; and great variations of 

 rate in cither direction may be produced. Thus 

 a certain degree of softness in the cushion may 

 make the chronometer lose considerably ; and a 

 still softer cushion may make it gain considerably ; 

 and cushions softer yet would make the chrono- 

 meter gain, although not so much. It is possible 

 that an improvement in the practical performance 

 of chronometers at sea may be attained by fixing 

 the outer case of the instrument to a very heavily 

 weighted base, this base being placed on an 

 ordinary cushion. 



At the conclusion of the paper, in answer to 

 questions by the PRKSIDKNT, Mr. DAY, and Mr. 

 DA vi SON, 



Sir \YM. THOMSON said that the weight of the 

 chronometer would influence the rate at which it 



