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Mr. P. E. Shaw : 



together, there being evidently some coherence or adhesion 

 between them at the place of contact. The contact surfaces 

 were varied, but the effect remained, in the cases of the 

 junctions copper-copper, copper-carbon, and carbon-carbon*. 



Such an arrangement as the above is obviously well 

 adapted to showing very minute forces of adhesion, if any such 

 exist, especially as the galvanometer used was a delicate 

 reflecting one. 



The phenomenon was then looked for, and found, in a 

 species of balance, having a beam made of a very light strip 

 of aluminium weighted at one end and having the contact 

 surfaces at the other end. 



As there seemed to be no satisfactory explanation forth- 

 coming, from any authority consulted, for the adherence thus 

 •doubly proved to exist, I determined to push the inquiry 

 further. The following arrangement was set up. 



2. The Aphometer. 



A D'Arsonval galvanometer was used. The coil BC 

 (fig. 1) is seen held by the phosphor-bronze suspensions AB 

 and CD, above and below it ; ABCD is in a vertical plane 

 with the contact wires ab, cb. The galvanometer mirror is 

 seen at B. The galvanometer circuit is A B C D F H and has 

 a shunt S across the terminals of the coil. But another 

 circuit, the contact circuit, is abcdef, quite insulated from 

 A B C D F Gr. The contact wires ab, cb can be fixed in the 

 binding-screws at a and c (or other wires can be substituted 

 for them easily, when required) ; but whereas ab is held 

 firmly by the galvanometer-coil and moves with it, cb is fixed 

 to the frame of the instrument and is rigid. The frame itself 

 and the strong permanent field-magnets are omitted. 



As regards the details of the circuits, the galvanometer 

 circuit has merely a cell, resistance-box, key, and shunt S ; 

 but the contact circuit is more elaborate : the cells have a 

 reversing-key attached to them; there is a galvanometer set 

 ;as a delicate ammeter (100 divs.=^ a); a voltmeter (showing 

 TU"o v * s P u ^ as a snun * across the terminals of the contact; 

 there is also a telephone introduced as shunt to a small 

 resistance in the circuit. By this arrangement, if any change 

 occurs in the resistance of the contact it can be written down 

 at once from the simultaneous readings of ammeter and 

 voltmeter. If now a suitable current is put on in the 

 galvanometer circuit, the wire ab can be brought round till it 



* The carbon used here was graphite. 



