x g Dr. Fordyce's Account 
Graham's clock, in order to adjust the length of the pendulum, 
but found irregularities frequently take place. I then adjusted 
it by observation, and soon found that Graham's clock went 
much more irregularly than my own. I adjusted it by turn- 
ing the head of the screw at L, fig. 4, until the clock came to 
lose seven-tenths of a second in 24 hours. I did not think it 
worth while to bring it nearer; I then began to observe, and 
carried on the observations, when the weather permitted, for 
about nine months, during which the thermometer had fallen 
so low as 15° of Fahrenheit, in the clock case, and risen as 
high as 84 ; and with considerable variations. Unfortunately 
I have mislaid or lost the particulars of each observation ; but I 
have preserved the greatest difference from the rate of its go- 
ing. Counting on, according to the rate of its going, during 
the whole time it never exceeded the sum, half a second, nor 
was ever less than half a second, whether it was taken from 
day to day, month to month, or from any one to any other 
period during the observation. 
Undoubtedly, therefore, notwithstanding the errors that 
might have arisen from the expansion of the wood by moisture, 
and from the unsteadiness of the building in which it was 
placed, it certainly performed better than any other time-piece 
that has been made ; and perhaps affords a principle whic l 
may be used in fixed observatories for keeping time with cer- 
tainty, by easy and not very expensive means; and of deter- 
mining, with the rest of Mr. Whitehurst’s apparatus, the 
difference between the lengths of two pendulums swinging 
equal arches of circles of different diameters, in any two given 
different times. 
The astronomer royal has also suggested an improvement: 
