652 PHILOSOPHICAL TRANSACTIONS. [aNNO 1734. 



The transits of the stars over the meridian were observed with a telescope, 

 fixed at right angles to an horizontal axis, whose ends lay exactly east and 

 west; by the turning of which axis, the line of collitnation of the telescooe 

 was constantly directed in the plane of the meridian. This instrument was 

 daily adjusted to a mark, fixed in the meridian; and in the journal, between 

 the 'id and 3d of February, the following remark was made. 



N. B. This day was hotter than usual, as appears by the thermometer; and 

 the transit instrument had lost the level a little; but after we had adjusted it, 

 it pointed exactly to our meridian mark; and therefore we are at a loss for the 

 cause of this difference in the clock. 



From the foregoing table it appears, that the clock lost 54"" 2V in 26 revo- 

 lutions of the stars; that is, about 2™ 5^" in one revolution; the difference 

 from this medium somewhat varying on account of a greater or less degree of 

 heat on different days. 



The mean of all the observed heights of the thcnnotnetcr, fioin Jan. 2t) to 

 Feb. 18, was about 12^ divisions; therefore the difference between the mean 

 heights of the thermometer at Jamaica and London, during the intervals of the 

 respective observations, was I5J divisions; the spirit standing so much higher 

 in Jamaica, because of the greater heat in that island. 



That we might be able to judge, how much the different degrees of heat, 

 corresponding to any number of divisions on this thermometer, would cause 

 the clock to go slower, by lengthening its pendulum, Mr. Graham took notice 



