Bbown. — Action of Fusible Cutouts. 363 



The resistances were measured near 15°, and corrected to 

 zero by the formula given in the paper for 0° C. (col. II.). 

 The temperatures in this are not corrected ; the thermometer 

 has been sent to Kew. The dimensions of the wires are 

 reduced to 0° C. by the coefficient (linear) 21 x 10- 6 . 



It will be observed that these figures, leaving out the very 

 thin wires, which are perhaps abnormal, do not vary much 

 (8-2 per cent.) from the value 10-4 x 10 — 6 ohms per cubic 

 centimetre at 0° C — that is to say, the common impurities 

 do not much affect the conductivities apparently ; also, that 

 the materials probably the most pure have the highest con- 

 ductivity, which is usually the case with metals. The agree- 

 ment with the Continental authorities is very fair, but with 

 the English there is a very decided disagreement. 



The values for specific gravity agree very well with those 

 of Matthiessen, which I calculate to have been 7 - 282, the 

 only notable exception being the " Cornish tin," which gives 

 a value about 1 per cent. high. 



It is now necessary to refer to the results of previous 

 experimenters, and here is the chief difficulty in making 

 original researches of this kind in Wellington. Beyond the 

 "Transactions and Proceedings of the Royal Society" (for 

 which I am indebted to Sir James Hector), and a few years 

 of the Electrician, which the Telegraph Department kindly 

 gave me access to, a few works in the public libraries, and 

 technical papers and works of my own, I found nothing 

 available in Wellington. This seems to me a regrettable state 

 of affairs. However, I think I am justified in asserting that 

 Sir W. Preece's tables have never been effectively criticized. 

 Dr. Bottomley, indeed, in a letter to the Electrician * sug- 

 gests that Sir W. Preece's figures were not in accord with 

 some experiments of his. I may extract a sentence: "And 

 I should expect that it would require currents greater for 

 small wires and smaller for large wires than corresponds to 

 the proportionality to d V d," which is what I have found. 

 But in a postscript he adds that a difference in the condi- 

 tions may alter the law in such a way as " would corre- 

 spond to what Mr. Preece has found, though, of course, the 

 subject will require investigation." The effect of this criti- 

 cism may be judged from the date (1884). 



Again, in 1892 Professor W. E. Ayrton, F.R.S., and Mr. H. 

 Kilgour made a research into the emissivity of platinum wires 

 up to 14 mils in diameter.! They write: "In 1884 it was 

 observed experimentally that, whereas the electric current 

 required to maintain a thick wire of given material under 



* 19th April, 1884, p. 541. 



f Phil. Trans. Roy. Soc, 183a, 1892, p. 371, et seq. 



