40 POPULAR LECTURES AND ADDRESSES. 



the square of the difference of temperature by 

 a certain constant co-efficient This constant co- 

 efficient and the temperature of maximum rate 

 remain the same for the same chronometer until 

 it is cleaned or repaired, or until it requires to be 

 cleaned or repaired. Thus, for example, a certain 

 chronometer, " J. Bassnett & Son, No. 713," after 

 being rated by Mr. Hartnup, was put on board the 

 ship Tenasserim, in Liverpool, December, 1873, for 

 a voyage to Calcutta. The result of Mr. Hartnup's 

 rating and the application of his method showed 

 that this chronometer had its maximum rate at 

 temperature 70 Fahrenheit, and that the difference 

 of rates at any other temperature, reckoned in 

 seconds or fractions of a second per day, was to 

 be calculated by multiplying the square of the 

 difference of temperature from 70 into '0034 sec. 

 Thus at 80 or 60, the chronometer would go 

 slower than at 70 by "34 of a second per 

 day ; at 90 or at 50 it would go slower than 

 at 70 by 1*36 seconds per day ; and so on for 

 other temperatures. 



The ship sailed from Liverpool on the 2ist of 



