432 



Dr. S. Bidwell. On the Changes of [Apr. 11, 



curve (d), fig. 4, it is seen to be quite insignificant. Since no experi- 

 ments have been made to determine the lifting-power of nickel, this 

 was calculated from the expression (27rl 2 + BJ)/g. Values of I were 

 obtained from a table given by Ewing, based upon results of an experi- 

 ment by Du Bois ;* the specimen used was an ovoid instead of a 

 cylindrical wire, but the values might be increased or diminished by 

 10 per cent, without influencing the corrected curve to any appreciable 

 extent. Young's modulus M was taken as 2*2 xlO 9 , approximating 

 2175 xlO 6 , the value found f for nickel by H. Tomlinson; this also 

 need not be very accurately known for the present purpose. Table IV 

 shows how the ordinates of the compression curve (P/220), and those 

 of the corrected curve (R- P/220), were determined. 



Table IV. 



P = (27rI 2 + HI)/#. C = P x 10 7 /M = P/220. R = retraction 

 in ten-millionths. 



H. 



I. 



P. 



C. 



E, 



E-C. 



100 



313 



659 



3 



136 



133 



200 



375 



977 



4-5 



181 



177 



300 



406 



1180 



5 3 



210 



205 



400 



428 



1348 



6-1 



224 



218 



500 



441 



1470 



6-7 



232 



225 



600 



450 



1572 



7-1 



239 



232 



700 



456 



1657 



7-5 



242 



234 



800 



459 



1724 



7-8 



244 



236 



1200 



1 



471 



1997 



9-0 



245 



236 



Curve (n) which nearly coincides with the thermoelectric curve (L) is 

 the uncorrected retractioD curve (k) inverted and plotted to the scale of 

 ordinates in the right-hand margin. If the corrected curve were 

 plotted to the slightly different scale just within the margin, it would 

 be substantially identical with (n), which may therefore be regarded as 

 representing either the corrected or the uncorrected curve of change of 

 length. 



The small difference noticeable in the forms of the two curves (O) 

 and (I) for the two nickel strips is just such as would be caused by the 

 difference between their dimensional ratios. 



As to the curves in fig. 9, which show a remarkable qualitative 

 correspondence with regard to the complex effects of tensile stress, 

 nothing need be added to what has already been said. The dotted 

 curves X are of course inverted. 



* ' Magnetic Induction,' 3rd edit., p. 164. 

 f ' Eoy. Soc. Proc.,' vol. 37, p. 390, 1884. 

 I ' Eoy. Soc. Proc.,' vol. 47, p. 475, fig. 3, 1890. 



