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o| a disc of a diameter approximating to that of the outer wall of the tnlx*. In the 

 centre of this disc ;i hole corresponding to the bore of the tube was punched, the 

 operations throughout being such as to prevent crinkling of the foil and fraying of 

 the edges. When connecting two tubes in series, this platinum ring was laid on one 

 of the ground faces, the two projecting strips bent over, and the ebonite collar B slid 

 and screwed into position. The strips were thus gripped between the collar and 

 tube, and the foil prevented from becoming excessively displaced. The corresponding 

 portion of the connector previously attached to the second tube was now combined 

 with A, and the junction rendered complete. In effecting this, neither tul>e is 

 necessarily rotated about its axis, but when completed, some sight rotation is, in 

 general, required to bring the two axes into line. An examination of the junction in 

 two directions at right angles is rendered possible by the circular holes in the 

 connector, although, as will presently lie seen, a second examination is requisite. 

 Once in their proper positions, the three tubes, comprising mercury standard and its 

 two connecting pieces, must have no relative rotation about their common axis. 



In practice, two other ebonite connectors joined the auxiliary tubes of the standard 

 to others bent at right angles and intended for battery leads. These connectors are 

 shown at c and d in fig. 7, and allow the leads e and f to freely rotate. 



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EffiD J 



Fig. 7. 



Smaller glass tul>es with short platinum leads passed into e and f, and others 

 similar to them served as conductors to the potential jx>ints of the standard. These 

 are shown at g and h. Glass vessels a little more than 5 centims. long and about 

 2'5 centims. diameter covered the junctions. At c and </ these vessels merely served 

 to insulate the points ; at a and b they were tilled with mercury, the platinum It-ads 

 dipping into the liquid. 



The general scheme followed in fitting and tilling the standard was as follows : 

 The tulxjs, and every part employed, were first carefully cleaned and dried, the parts 

 having appropriate markings for their filial positions. The junctions at a and h writ- 

 n. At rH'crtcd. tin- axes m.,<l.- to nearly coincide, and the four glass vessels slid ovn 

 the connectors so ;IN t-i i,st <>u the standard tube. The junctions c and / \\.n- m-xt 

 made (without platinum foil), and allerwards the four vessels were passed into position 



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