Curiosities of Science. 



During the first 6 weeks it gained 13m 20", answering to 3 20' of longitude. 

 In the 2d period of 6\ 



weeks (from Aug. 6 to L 8 17 24 



Sept. 17) 

 In the 3d period (from") 10 ^ o QI 



Sept. 17 to Oct. 29) ) " 

 In the 4th period (from ") 1 o 9 Q 



Oct. 29 to Dec. 20) j " 12 26 

 In the 5th period (from\ K 40 1 OK 



Dec. 20 to Jan. 21) J 

 In the 6th period (from \ in p, o 4 q 



Jan. 21 to Mar. 4) / " 



It was thence concluded that Mr. Harrison's watch could 

 not be depended upon to keep the longitude within a West- 

 India voyage of six weeks, nor to keep the longitude within 

 half a degree for more than a fortnight ; arid that it must be 

 kept in a place where the temperature was always some degrees 

 above freezing.* (However, Harrison's watch, which was made 

 by Mr. Kendal subsequently, succeeded so completely, that after 

 it had been round the world with Captain Cook, in the years 

 1772-1775, the second 10,000 was given to Harrison.) 



In the Act of 12th Queen Anne, the comparison of chrono- 

 meters was not mentioned in reference to the Observatory duties ; 

 but after this time they became a serious charge upon the Ob- 

 servatory, which, it must be admitted, is by far the best place 

 to try chronometers : the excellence of the instruments, and the 

 frequent observations of the heavenly bodies over the meridian, 

 will always render the rate of going of the Observatory clock 

 better known than can be expected of the clock in most other 

 places. 



After Mr. Harrison's watch was tried, some watches by Earn- 

 shaw, Mudge, and others, were rated and examined by the As- 

 tronomer-Royal. 



At the Royal Observatory, Greenwich, there are frequently 

 above 100 chronometers being rated, and there have been as 

 many as 170 at one time. They are rated daily by two ob- 

 servers, the process being as follows. At a certain time every 

 day two assistants in charge repair to the chronometer-room, 

 where is a time-piece set to true time ; one winds up each with 

 its own key, and the second follows after some little time and 

 verifies the fact that each is wound. One assistant then looks 

 at each watch in succession, counting the beats of the clock 

 whilst he compares the chronometer by the eye ; and in the 

 course of a few seconds he calls out the second shown by the 

 chronometer when the clock is at a whole minute. This num- 

 ber is entered in a book by the other assistant, and so on till 

 all the chronometers are compared. Then the assistants change 



* In trying the merits of Harrison's chronometers. Dr. Maskelyne acquired 

 that knowledge of the wants of nautical astronomy which afterwards led to the 

 formation of the Nautical Almanac. 



