366 Transactions. — Chemistry and Physics. 



problem which interests insurance companies, electrical en- 

 gineers, and users of electricity alike. 



I do not think it reasonable that private individuals should 

 be expected to carry out work of this kind at their own ex- 

 pense, but I shall be content if I have been able to do some- 

 thing towards the conversion of the fusible cutout from an 

 empirical makeshift to a scientific instrument. 



In conclusion, I would like to thank Mr. Stuart Richard- 

 son, A.M.I.E.E., of the New Zealand Electrical Syndicate, 

 for the loan of measuring-instruments and the use of standard 

 instruments for the calibration of the same. 



Note. — I have taken out values for emissivity from the re- 

 search of J. E. Petavel (loc. cit.), and find that they agree 

 very well with my curve. The points are marked in triangles 

 on the chart. The following are the figures (emissivity at 

 200° C. of platinum wires) : — 



Diameter 



(Mils). e - 



4415 ... 0001 in horizontal iron tube. Inch. Int. Diam. 



44-15 ... 000108 in horizontal brass box, l^in. x 3 in. x3in. 



23-7 ... 000148 in horizontal brass box, l^in. x 3 in. x3in. 



Mr. Petavel also gives a figure from Dr. Bottomley's re- 

 searches'" of a vertical wire, which he calculates at about 



0'8137 



11-8 mils, for which e = ' = 0001995, which value, plotted 



back on Mr. Petavel's curves, fig. 7 reduces to about 000165. 

 Then, adding 30 per cent, (to express the difference between 

 a wire vertical and horizontal, estimated from the same 

 curves), we have € = 0002145. This value is plotted in a 

 square, and is given for what it is worth. 



Dr. Bottomley in this paper gives results, which I take 

 as the lowest value of e attained by himself, as 45 x 10 ~~ 6 , 

 and as 30 x 10 — 6 by Schliermacher, in the best vacua obtain- 

 able. 



I have taken a value of c for a ^in. copper rod at 

 200° C. from Mr. R. W. Stewart's results,! for which 

 c = 0000387, about ; also a value from an engineering-book 

 of e = 0-000245 for a steam-pipe at about 150° C. These 

 have been plotted in as figures of comparison ; Mr. Box's 

 formula (€ = 00005710 x 0833 D-i), which is referred to 

 by Professor Ayrton and Mr. Kilgour, for large cylinders at 

 a temperature not given. 



These results, plotted together, suggest a curve for € of 

 some fractional power of D — 1 , with zero at c = 000005, 



•Phi'. Tran=., 178a, 1887. 

 t Phil. Trans., 184a, 1893. 



