VOL. XXXVIII.J PHILOSOPHICAL TRANSACTIONS. 051 



TIlis experiment shows, that a small difference in the arcs, described by the 

 pendulum, or a small alteration in the weight that keeps it in motion, will cause 

 no great difference in the duration of the vibrations, and therefore a little alte- 

 ration in the tenacity of the oil on the pivots, or in the foulness of the clock, 

 will not cause it to accelerate or retard its motion sensibly ; from whence we 

 may conclude, that whatever difference there shall appear to be, between the 

 going of the clock at London and in Jamaica, it must be entirely owing to the 

 lengthening of the pendulum by heat, and the diminution of the force of gra- 

 vity on it. 



Mr. Graham sent very full directions to Mr. Campbell, describing in what 

 manner the clock was to be fixed up, and how the pendulum might be reduced 

 exactly to the same state as it was when in England; but no intimation was 

 given concerning the going of the clock, that the experiment might be made 

 with all possible care, and without any bias or prejudice in favour of any hypo- 

 thesis, or former observations. 



In July 1732 was received an account of the success of the experiment, by 

 the hands of Mr. Joseph Harris, who was present at the making of it in 

 Jamaica, and who brought over with him the original journal of the observa- 

 tions of the transits of two stars, viz. Sirius and |3 Canis majoris, over the 

 meridian, compared with the clock, after it was fixed up in Jamaica, as Mr. 

 Graham had directed ; with the height of the spirits of the aforesaid thermo- 

 meter, on the several days of observation. 



The chief of those observations are contained in the following table; the 

 first column shows the day of the month; the second the name of the star, 

 and the time by the clock of its observed transit over the meridian; the third 

 contains the hour of the day, when the thermometer was observed, with the 

 height of the spirits at those hours; the morning hours being denoted by the 

 letter a, and those of the afternoon by the letter p. 



