290 



Mr. W. H. Preece. 



[Dec. 22, 



The conclusions derived from these experiments were that the best 

 metal to nse for small diameters was platinum, and for large wires 

 tin. Platinum fuses in a wax-like kind of way without explosion or 

 scattering of molten particles. Platinum has great advantages over 

 other materials ; it neither tarnishes nor deteriorates. It is easily 

 soldered. 



Tin behaves very much in the same way when its dimensions are 

 large. But it is very questionable whether large wires should ever 

 be used for fusible cut-outs. Owing to radiation the surface keeps 

 cool and solid, while the centre is molten and liquid. It bursts 

 with an explosion, and the incandescent particles are forced away 

 radially in all directions with considerable energy. 



Fusible cut-outs are effective but somewhat barbarous, and from 

 the absence of any scientific enquiry into their character and jndg- 

 ment in their use, they have in the majority of instances become 

 rather a source of danger than of safety. 



Series III. 



The third series of experiments was made to determine the constant 

 " a " when each wire was 6 inches long and therefore free from any 

 cooling effect of the terminals. 



Copper. 



Diameter 

 in 

 inches. 



Actual 

 fusing 

 current m 

 amperes. 



Fusing 

 current 

 calculated. 

 ad 3 ?. 



Constant 



" 



-004 



3 253 



2 -95B 



12888 



0-005 



4 "444 



4-130 



12569 



0'007 



7-618 



6 842 



13007 



o-oio 



13-33 



11 -684 



13330 



0-013 



15-55 



17-32 



10491 



0*014 



17-14 



19 35 



13835. 



018 



25 -55 



28-22 



10580 



0-020 



27-77 



33 -04 



9818 



0-023 



35 -55 



40-75 



10192 



0-030 



52 -69 



60-71 



10140 







Mean = 



11684 



