1-J4 DR. R II- CKIFFITHS AND MR. EZER GRIFFITHS ON THE 



As the left-hand portion is a replica of the right, it will suffice to describe the 



latter only. 



The metal (A), whose capacity for heat was to be determined, was cast and then 

 " turned" into the form of a cylinder 15'2 cm. long and 57 cm. in diameter. 



This cylinder fitted accurately into a thin copper case (C) of mass, apart from the 

 lid, of 149 grms. Thus the actual radiating surface surrounding the metal blocks was 

 similar throughout all experiments. 



Two small copper pins attached A in its proper position to the copper lid to which 

 the case was fastened by a copper ring bearing a screw thread. 



Three quartz tubes passed through the brass pipes fixed in the lid of the external 

 case, and supported the copper case and block within the outer brass cylinder. 



These quartz tubes having been previously platinized were soldered at their lower 

 ends into short copper ferrules which formed parts of the copper lid and at their upper 

 extremities to the top of the brass tubes which, for 7 cm. of their length, were washed 

 by the tank liquid. 



Between the case-lid and the outer brass lid a mica disc of nearly the diameter of 

 the brass cylinder was placed and through it passed the three quartz tubes. 



After the metal block had been fixed in its case and pins and ring firmly screwed 

 home, the case and contents were lowered into the outer brass vessel, the edges of the 

 mica disc (which were slightly padded with cotton wool) resting on a projecting 

 circular ring (H) about 3'5 cm. above the top of the copper lid. Thus the effect of 

 the flow of convection currents from inner to outer case, or vice-versd, was 

 diminished. The brass lid was firmly screwed down over a lead ring by eight bolts. 



After the parts were assembled, the air-tightness of the apparatus was ascertained 

 both by pressure and exhaust tests. The lateral clearance between the inner and 

 outer cases was 2 cm. ; the vertical, between the lids, 6 '5 cm. ; and between the 

 bases, 6 '5 cm. 



The volume of air contained in the brass case after insertion of the metal block was 

 about 1500 c.c. A pressure gauge containing a light oil was connected by means of 

 a 3-way tap with one of the tubes leading from this case to the exterior of the tank. 

 Observations of the air pressure within the case were taken immediately before and 

 after an experiment. The air being slightly warmed, the pressure rose during that 

 interval, and thus the presence of any leakage could be detected. 



The annular air space could be regarded as the bulb of a constant volume _ 

 thermometer, and from the change in pressure during an experiment, the change i 

 the average temperature of the enclosed air could be deduced. 



It was found that this change was about one-sixth of that of the contained block. 



The approximate magnitude of any correction rendered necessary by the capacity 

 for heat of the contained air could thus be ascertained (see Section VI.). 



In our preliminary experiments the copper case was placed within specially 

 11 vacuum vessels," the exterior walls of which fitted closely into the 



air 

 in 



