Stress and Strain on the Properties of Matter. 



505 



The density of the metal was determined by means of a specific 

 gravity flask, some pieces having been previously broken off for the 

 purpose, and was found to be 8'231 at a temperature of 16° C. The 

 same pieces were well annealed, and the density at 16° C. was then 

 found to be 8"259. The mean section as determined from the mass of 

 the strip 29*65 grams, the length, and the density, was for the unan- 

 nealed metal 0*06168 square centimetre, and this value, agreeing as 

 it did fairly with that got by gauging, was assumed to be correct. 



The modulus of longitudinal elasticity was determined by holding 

 the strip in the centre and rubbing it along its length with a resined 

 glove. The note obtained was very high in pitch, but the results of 

 the measurements of the number of vibrations obtained by the use of 

 the syren agreed very well with each other.* 



Experiment I. 



The lower double octave obtained by rubbing the strip longitudi- 

 nally was taken on a monochord ; the syren was then raised to the 

 pitch of the monochord, and the number of vibrations counted for 

 two minutes at a time. 



Number of 



Number of vibrations recorded 



trial. 



by the syren in two minutes. 



1 



6286 x 20 



2 



6273 . . . 



3 



6273 . . . 



Mean 



6277 x 20 



In this experiment the monochord was retuned twice, and it will be 

 observed that the mean value does not differ from any of those forming 

 it by so much as 0'15 per cent. From these last observations the value 

 of " Young's modulus " for the unannealed cobalt was ascertained to be 

 2005 X 10 6 grams per square centimetre. The same strip was then 

 well annealed, and three results, equally as concordant as the last, 

 were obtained when the strip was thrown into longitudinal vibrations. 

 The value of "Young's modulus" of the metal in the annealed con- 

 dition was 1817 X 10 6 grams per square centimetre. 



Arrangement of the Cobalt Strips for Observation on the Alteration of 

 Resistance produced by Longitudinal Traction. 



The two strips (see fig. 1) in the first instance in the unannealed con- 



* I have again to thank Mr. Furse, of King's College, for his assistance here. 

 VOL. XXXIX. 2 L 



