262 Mr. G. Gore on a momentary [Jan. 28, 



at the other end to the hook L (see fig, 2). The cylindrical binding- 

 screw I has a hook by which it is attached to the loop M (fig. 2). N is 

 an axis suspended delicately upon centres, and carrying a very light index 

 pointer O. The hook L and loop M are separate pieces of metal, and move 

 freely upon an axis, P (fig. 2). The distance from the centre of the axis 

 N to that of P is 12*72 millimetres ( = 0*5 inch), and to the top of the 

 index pointer 25*45 centimetres ( = 10*0 inches) ; every movement hori- 

 zontally, therefore, of the loop M is attended by a movement, twenty times 

 the amount, of the top of the pointer. Q is a screw for supporting the axis 

 N. I have found it convenient to put the zero-figure of the index towards 

 the left-hand side of the index-plate. H is a separate piece of wood fitting 

 into a rectangular hole in the base board ; it carries a graduated rule, S, for 

 measuring the length of the wire to be heated, and is easily removed, so 

 that the wire may, if necessary, be heated by means of a row of Bunsen's 

 burners. The rule T is used when measuring the amount of strain. U is 

 a vertical stud or pin of brass (of which there are two) for limiting the 

 range of movement of the pointer O. 



In using this apparatus, a straight wire or ribbon, H, of a suitable length 

 and thickness was inserted, the index pointer brought to by adjustment 

 of the sliding-wire G, and a suitable amount of strain (varying from less 

 than two ounces to upwards of twenty) put upon the wire by adjusting the 

 sliding hooked wire E. One pole of a voltaic battery, generally consisting 

 of six Grove's elements, was connected with the binding-screw C, and the 

 other pole then inserted in the mercury-cup of B. As soon as the needle 

 O attained a maximum or stationary amount of deflection, the battery-wire 

 was suddenly removed from B, and the wire allowed to cool. The mover 

 ment of the needle O was carefully watched both during its movement to 

 the right hand and also during its return, to see if any irregularity of motion 

 occurred. 



Wires of the following metals and alloys were employed : — palladium, 

 platinum, gold, silver, copper, iron, lead, tin, cadmium, zinc, brass, german- 

 silver, aluminium, and magnesium ; metallic ribbon was also employed in 

 certain cases. 



In these experiments the thickness and length of the conducting-wire or 

 ribbon had to be carefully proportioned to the quantity and electromotive 

 power of the current, so as to produce in the first experiments with each 

 metal only a very moderate amount of heat ; thinner (and sometimes also 

 shorter) wires were then successively used, so as ultimately to develope 

 sufficient heat to make the metal closely approach its softening or fusion- 

 point. The battery employed consisted in each case of six Grove's cells, 

 each cell containing two zinc plates 3 j inches wide, and a platinum plate 

 3 inches wide, each immersed about 5 inches in their respective liquids. 

 The amount of tension nn parte d by the elastic band required to be care- 

 fully adjusted to the cohesive power of each metal ; if the stretching 

 power was too weak, the phenomenon sought for was not clearly deve- 



