164 Messrs. Bottomley and Tanakadate* on the 



quantity of metallic tungsten remains in the alloy, yet the 

 properties of the substance are in many respects remarkable. 

 The metal is capable of being polished so as to be almost as 

 beautiful as silver in appearance, having only a slightly darker 

 and more steel-like colour ; and when it has been polished it 

 remains absolutely untarnished even in the atmosphere of a 

 large town, for years at any rate. It has very remarkable 

 properties as to electric resistance. It possesses a very high 

 resistance, while at the same time it has a much lower tempe- 

 rature-variation of electric resistance than any other known 

 metal or alloy. It has also, as Sir William Thomson has found, 

 very excellent elastic qualities. 



Although it was not proposed to use the platinoid with any 

 metal other than platinmn in the investigation on thermal 

 radiation above referred to, it nevertheless seemed advisable, 

 when these experiments were being undertaken, to determine 

 its position with respect to some other metals. It was accord- 

 ingly tried as a pair with platinum, iron, aluminium, and with 

 two specimens of copper. 



A low-resistance Thomson's reflecting-galvanometer was 

 specially prepared for the purpose of the experiments. The 

 mirror was a plane parallel mirror of very excellent quality, by 

 Steinheil of Munich. Its deflexions were observed by means 

 of a telescope with cross-wires and scale, instead of with lamp 

 and scale. To avoid any influence of the suspending fibre 

 (which even though of single cocoon-silk fibre does with 

 short fibres give an appreciable torsional resistance) the 

 mirror was suspended % by spider-line. The suspending of a 

 mirror, weighing with its magnet 0*2 gram, by a single 

 spider-line is a matter of some nicety and difficulty ; but 

 when it has been accomplished the result is so thoroughly 

 satisfactory that it is easily admitted to be well worth a morn- 

 ing's labour. 



To make the suspension, two small pieces of very thin 

 bristle or of hard-spun silk fibre or split horsehair are attached 

 to the ends of a suitable length of spider-line recently spun by a 

 good large spider*. By means of these attachments, which are 

 easily seen, the spider-line can be handled. It is then brought 

 over the galvanometer-mirror ; and great assistance is expe- 

 rienced in these operations, and in operations with single silk 

 fibres, by performing them on the top of a piece of looking- 

 glass laid on the table. The illumination from beneath of the 

 fibres makes it easy to do with these fine filaments that which 

 is otherwise scarcely possible. The fibre is attached to the 



* The body about as large as a pea. 



