Beown. — Action of Fusible Cutouts. 



367 



about, for average surfaces. Such a curve sketched in gave 

 the following trial ordinates: — 



Ayrton's formula gives 0154 for D -1 == 10. 

 The column " e calculated " is of values of e calculated 

 thus : — 



€ = 000005 + 0-010865 (D-i) -6.^5, D being mils. 



As will be seen, the agreement is fairly good as a first 

 approximation. 



The corresponding curve has been traced (thin line), 

 marked " B formula." It will be seen to agree in a rough way 

 with the data I have here collected, except for the copper 

 rod and steam-pipe, and also with Professor Ayrton and Mr. 

 Kilgour's results for wires finer than 2-7 mils, which could 

 not be plotted on the diagram. It will be observed that Mr. 

 Box's formula is parallel or tangential to it at 092 in. dia- 

 meter, my own straight-line formula at about 50 to 

 and the formula of Professor Ayrton and Mr 

 7 or 8 mils (about the mean diameter of the wire 

 them). 



It would appear from Dr. Bottomley's and Mr. Schlier- 

 macher's researches that the radiation, or electro-magnetic 

 emission, is not more than 000003 for silver or platinum tested 

 in vacua. This is not of very different dimensions to the con- 

 stant of Box's formula. Consequently, I take it, practically, 

 the whole of the emission from ordinary fuse-wires is convec- 

 tive. 



As this matter has been elaborated, I wish to again say that 

 my figures are subject to correction, chiefly for thermometer 

 error, especially for the three finer wires (those for which 

 D-i = 0-049, 0-068, and 0-1258), the physical constants of 

 these wires not yet having been determined. 



70 mils, 

 at 

 used bv 



Kilgour 



