On the Compressibility of Solids 



381 



observers are necessary, namely, one for each microscope, and 

 one to raise and relieve the pressure and observe the manometer. 

 I was fortunate in being assisted during this investigation by 

 Mr Andrew Kiiii:. who was formerly my regular assistant, and is 

 now of the Heriot-Watt College, Edinburgh, and by Mr J. Reid, 

 Demonstrator in the chemical laboratory of that institution. 

 These gentlemen gave up their Christmas vacation for this 

 work, and I owe them a deep debt of gratitude for the willing- 

 ness and the efficiency of their help. The metals experimented 

 with have been used in the form of wire, and the size chosen 

 22 of the standard wire gauge (S.W.G.). In the case 

 of aluminium, however, the size was No. 20. The dimensions 

 corresponding to those numbers are given in the following 

 table : 



degree in which the actual wires corresponded with the 

 tabular specification was checked by weighing measured lengths 

 of them. The weight of I metre of each wire was as follows: 

 I'l.itinum, 8-156 grammes; gold, 7-320 grammes; copper, 3-375 

 grammes; aluminium (No. 20), 1-642 grammes ; and magnesium, 

 *55 2 gramme. Neglecting tin- magnesium which. 1 

 pressed and not drawn, is very uneven in its calibre, these 

 figures show that the actual wires were very slight Iv -mailer 

 than they should be by the gauge. Tim-, in the case of the 

 platinum wire I c.c. occupies 2-636 metres (lineal) instead of 

 2-519 metres as by the tall< . 



platinum and gold wires were pure specimens obt. 

 i Messrs Johns**: hey in t i 1880. 



copper was "high c<i copper, 



aluminium and ma^nr-ium unes were of the best quahtv 

 obtainable at the present day. The platinum and gold wires 



