Calibrating Fine Capillary Tabes. 387 



The measurements of resistance were made with a metre 

 bridge with resistances lengthening it to 10 metres and a 

 resistance-box that had been carefully calibrated. The 

 accuracy of the measurement far exceeded the accuracy with 

 which the resistance could be kept constant. 



The arrangement of the capillary tube is shown in fig. 1. 



Fig. 1. 



An airtight joint with the side-tube A and B is made by 

 means of the two rubber plugs, RR. To fill the tube, the 

 limb A is half-filled with mercury and closed with a rubber 

 plug. It is then turned upside down, fig. 2, and exhausted 



Fig. 2. 



.0 CUT j3H.rn.|). 



through B by means of an air-pump. On inverting the tube 

 and removing the plug from A, the mercury was forced 

 through the capillary into B. 



In making the measurements, connexion is made by 

 means of stout, copper wires dipping into the arms A and B, 

 which are half-filled with mercury. The two rubber pings 

 BR were dispensed with in later experiments by grinding 

 the tubes roughly together, and then cementing them with a 

 small quantity of Schcenbeck enamel. 



