Temperature of Wires under Pulling Stress. 95 



tions through the impossibility of controlling the temperature 

 of the tube in which the wires are placed. If, for example, 

 there is any difference as to expansion with temperature of 

 the same wire when lightly and when heavily loaded, a cause 

 of disturbance would be introduced which it would be ex- 

 cessively difficult to allow for. It seemed therefore absolutely 

 essential to make direct experiments on this point. The 

 object of the present communication is to give an account of 

 some experiments of this kind. A preliminary account of 

 these experiments was communicated to the British Associa- 

 tion at the Manchester meeting (1887), and was printed in 

 the Philosophical Magazine for October of that year. 



The wires hung up in the tower of the Glasgow University 

 building are two of platinum, two of gold, and two of palla- 

 dium, these wires being chosen on account of their small 

 liability to oxidation. The wires on which I have experi- 

 mented up to the present time have, however, been of copper 

 and platinoid. The latter metal is an alloy* of nearly the 

 same composition as German silver, but containing a small 

 quantity of tungsten and made in a peculiar way. 



The figures show the arrangements for experimenting. A 

 long tube of tin-plate about 2 J inches in diameter was set up 

 vertically, fixed by means of brackets at two or three places. 

 This tube has inlets and outlets for steam, of which I have a 

 plentiful supply in the laboratory from boilers connected 

 with the University apparatus for heating and ventilation. 

 It has also openings for thermometers. The length of the 

 tube was 17^ feet in the experiment with copper wire, and 

 somewhat shorter in the platinoid experiment. 



A piece of excellent copper wire was taken, and its break- 

 ing weight was found to be 750 grammes. Its diameter was 

 022 millim. Two portions of this wire were hung side by 

 side in the centre of the tube. In order to suspend them 

 their ends were passed into two small trumpeted holes in a 

 stout brass plate and soldered to the back of the plate. The 

 plate was screwed up to a strong beam in the ceiling of the 

 laboratory. This forms by far the best mode of supporting a 

 wire for experiments on elasticity. One of the wires carried 

 75 grammes, the other 375 grammes. 



A few preliminary experiments as to heating and cooling 

 revealed a difficulty the magnitude of which I was unprepared 

 for. When the steam was admitted into the tube the wires 

 of course expanded, the heavily loaded wire going dow T n 

 far more than the other ; and when the steam had been 

 stopped and the tube allowed to cool, they contracted again 

 * Invented and patented by Mr. F. W. Martino of Sheffield. 



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