36 



has left behind him in the Philosophical Transactions a detailed 

 account of the various experiments which resulted in the invention 

 ofthe "mercurial compensating pendulum," which consisted of a 

 rod of steel of the requisite length, but instead of having a leaden 

 bob at the end, he adopted a glass cylinder, containing a given 

 quantity of quicksilver, a metal singularly sensitive to changes of 

 temperature. 



The effect of such a combination is at once apparent. If the 

 temperature increases, the rod lengthens downwards, but the 

 column of mercury lengthens upwards, and the centre of gravity 

 remains unaltered. On the other hand, if the temperature falls, 

 the rod shortens upwards, but the column of mercury shortens 

 downwards, and again the centre of gravity remains unaltered. 



As I have before remarked, the combination of these two 

 inventions of Graham, at once raised the clock from the position 

 of a useful article of furniture, to that of a scientific instrument of 

 the highest value; and so thorough was the quality of his work- 

 manship, that there is to this day in the Greenwich Observatory a 

 clock by Graham in daily use, which must be about 140 years old 

 the performance of which, even yet, is on a par with that of any 

 other in the establishment. 



But it is not as a means of regulating a clock with accuracy 

 only that the pendulum has rendered great services to science; it 

 has been used with wonderful success, by watching its oscillations 

 m different latitudes, to determine the exact figure of the earth, and 

 more recently, by the Astronomer-Royal, for the no less important 

 purpose of weighing the earth, by watching its oscillations on the 

 surface, and at the bottom of a deep coal shaft at Harton Colliery, ' 

 m the county of Durham, with a result probably more accurate than 

 those arrived at by other methods. 



Graham also was the first watch-maker of his day, and no 

 dandy of the period considered his personal adornment complete 

 unless he possessed one of his repeaters. In 1 753, the " London 

 Magazine" contains a poetic effusion, which describes the ingredi- 

 ents required in the manufacture of a fop :— 



