424 



DR. F. NORTON ON THE MODULUS OF TORSIONAL RIGIDITY OF 



which were some 30 centims. away, were soldered on to the wires from the galviiim- 

 meter, the junctions being enclosed in a water-jacket, through which a stream of 

 water at a known constant temperature was kept circulating. 



Pt-Rh. 



Fig. 5. 



In order that the soldered junctions of the quartz rods B and C with the metal 

 rods D and E should not get heated, two small water-jackets were fitted near the 

 ends of the platinum tube. These surround the tube at the parts containing the 

 soldered joints and effectively prevent its temperature from rising. The water- 

 jackets are two brass tubes, 2'5 centims. in diameter and about 5 centims. in length. 

 The lower end of the top jacket and the upper end of the bottom jacket are made of 

 copper, 5 millims. thick, and these fit tightly round the platinum tube, the junction 

 being made watertight by means of a thin layer of CHATTERTON'S cement on the 



