338 



Scientific Proceedimis^ Roiial Dublin Society. 



Then calling F = the fatigue of the wire, 



D = tlie unfatigiied steady deflection or twist, 

 d = tiie fatigued steady deflection or twist. 



D 



Tlie nickel wire wlien first tested was in the physical state in which it came 

 from the manufacturer. Its simple rigidity was about 800 x 10" grammes per 

 sq. cm., and when hung up inside the solenoid, with a certain load on its lower 

 end, and tested as explained above, it gave no deflection or twist when the 

 direct currents were sent round tiie solenoid, and through the wire ; nor was 

 there any humming sound in the solenoid when the alternating magnetic 

 field was applied, tliat is, the wire was too hard to be magnetised by the 

 magnetic field used. 



The wire was then taken down and hung vertically and loosely under 

 its own weight only and heated once from the top downwards to a dull red 

 heat by means of a broad Biinsen burner ; when cool its surface was cleaned 

 with fine emery cloth, its rigidity again tested and found to be about 

 790 X 10° grammes per sq. cm. The wire was then put up inside the 

 solenoid, and tested for fatigue as explained above ; the results obtained are 

 shown in Table I. Three loads were employed for each of tlie three values 

 of tlie rigidity ; in the tables below the longitudinal loads on the wires are 

 in the top horizontal line, and are of values I'O x 10^ ; 1*5 x 10*, aud 20 x 10* 

 grams, per sq. cm , the left hand vertical column gives the time in minutes 

 that the alternating magnetic field was round tlie nickel wire, and the letters 

 d and i'' represent the deflection or twist, and the fatigue respectively. 



Table I. 

 Kigidity = 790 x 10" grammes per sq. cm. 



