224 Mr. W. Sucksmith : Application of Ultra-Micrometer to 



rods. To the left-hand one is attached a polished steel eon- 

 denser-plate A, 17 sq. cm. in area and about 5 mm. thick, 

 and insulated from the supporting rod by a thin sheet of 

 mica. The distance separating the two condenser-plates can 

 be varied by a bending couple applied by placing weights 

 in the pan K which hangs from the graduated quartz 

 rod ML. The right-hand condenser-plate B is made of 

 polished aluminium 2 mm. thick, and is rigidly attached 

 to the end of the copper rod CD (which is shown enclosed in 

 non-conducting materials) the change in temperature of 

 which is to be measured. 



The method is as follows. Initially the scale-pan P is 

 empty. The heterodyne note in the telephone is adjusted by 

 means of an auxiliary condenser in the second circuit to be 

 within 2 beats per second of the note produced by the fork. 

 The copper rod, which is hollow, is heated electrically, thus 

 bringing the aluminium plate B nearer to A. Weights are 

 then placed in the pan until the same number of beats a& 

 before are heard in the telephone. 



A knowledge of the weight required to produce a certain 

 lateral shift of the plate A,, together with the expansion 

 coefficient of the specimen of copper used, enables the rise of 

 temperature to be determined. 



Fig;. 2. 



A cross-section of the expansion part of the apparatus is 

 shown in tig. 2. F is the hollow copper tube, which was 

 4 inches in length and embodying as little material as was 

 consistent with rigidity. Two pieces of quartz QQ were 



