1869.] On the Development of Electric Currents, fyc. 265 



behaved like those of copper in expanding regularly until a maximum was 

 attained, and then contracting slightly to a definite point whilst the battery 

 remained connected ; on stopping the current they contracted without irre- 

 gularity. When examined at lower temperatures, with a greater degree 

 of strain, no irregularity was observed. Various wires of aluminium were 

 examined ; the most suitable was one 0*88 millimetre thick, 20*4 centi- 

 metres long, with a strain of 12^ounces"; no irregularity was observed at 

 any temperature below redness ; aluminium expanded and cooled very 

 slowly, but less so than cadmium. Various wires and ribbon of magnesium 

 were also examined below a red heat, but no irregularity of cohesion, ex- 

 cept that due to gradual softening by heat, was detected. 



All the metals examined exhibited gradual loss of cohesion at the higher 

 temperatures if a suitable strain was applied to develope it. It is probable 

 that if the fractions of time occupied by the needle in passing over each 

 division of the index were noted, and the wire perfectly protected from 

 currents of air, small irregularities of molecular or cohesive change might 

 be detected by this method ; cadmium and zinc offer a prospect of this 

 kind. 



This molecular change would probably be found to exist in large masses 

 of wrought iron as well as in the small specimens of wire which I have 

 examined, and would come into operation in various cases where those 

 masses are subjected to the conjoint influence of heat and strain, as in 

 various engineering operations, the destruction of buildings by fire, and 

 other cases. 



IV. " On the Development of Electric Currents by Magnetism and 

 Heat." By G. Gore, F.ft.S. Received November 14, 1868. 



I have devised the following apparatus for demonstrating a relation of 

 current electricity to magnetism and heat. 



A A, fig. 3, is a wooden base, upon which is supported, by four brass 

 clamps, two, B, B, on each side, a coil of wire, C ; the coil is 6 inches long, 

 1 \ inch external diameter, and f of an inch internal diameter, lined with 

 a thin glass tube ; it consists of 18 layers, or about 3000 turns of insulated 

 copper wire of 0*415 millim. diameter (or size No. 26 of ordinary wire- 

 gauge) ; D is a permanent bar- magnet held in its place by the screws E, E, 

 and having upon its poles two flat armatures of soft iron, F, F, placed edgewise. 

 Within the axis of the coil is a straight wire of soft iron, G, one end of 

 which is held fast by the pillar-screw H, and the other by the cylindrical 

 binding- screw I ; the latter screw has a hook, to which is attached a vul- 

 canized india-rubber band, J, which is stretched and held secure by the 

 hooked brass rod K and the pillar-screw L. The screw H is surmounted 

 by a small mercury cup for making connexions with one pole of a voltaic 

 battery, the other pole of the battery being secured to the pillar-screw M, 



VOL. XVII. U 



