370 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



follows that a clock properly regulated at a mean temperature will 

 lose in summer and gain in winter. 



How is this defect to be remedied ? or how may it be diminished 

 so as to secure an invariable length of pendulum, and the isoclironism 

 of its oscillations ? This is accomplished by availing ourselves of the 

 unequal dilatation of various metals, and by compensating for the 



y 



Via. 253. Gridiron pendulum. 



FIG. 254. Leroy's compensation pendulum. 



lengthening which would lower the centre of oscillation by raising 

 that centre. Whence the name of compensation pendulums given to 

 the various combinations which have been invented. 



The method commonly used upon the Continent is the frame or 

 gridiron pendulum invented by Harrison. The rod is formed by a series 

 of alternate bars of brass and steel, jointed by transverse pieces, so that 



