200 On the Magnetic Elongations of Rods of Iron and Steel. 

 of — 8 — of an inch, while the smallest pass within the limits 

 of visibility of the most powerful microscope, being on ty Yo1)Voo 

 (or -000005) of an inch, and, furthermore, when it is known 

 that the last-mentioned quantity equals the change in length of 

 one of the rods caused by a variation of temperature of only 

 ToVd °^ a degree Centigrade, the difficulties I have conscien- 

 tiously met and surmounted in this delicate research become 

 manifest ; but the very knowledge of these difficulties has tem- 

 pered with modesty the confidence I feel in my work, and I will 

 gladly accept any correction my measurements may receive from 

 more experienced hands. 



Tables of the Elongations and Retractions of the Rods. 



Table I. — Elongations and Retractions in Units of the Tele- 

 scope-scale. 



A. 



B. 



C. 



D. 



E 



F. 



Rod. 



1st make- 



1 st break- 



Permanent e 



2nd make- 



2nd break- 



circuit. 



circuit. 



or r. 



circuit. 



circuit. 



1 



1-25 ef 



75 r 



•4ef 



'7ef 



•7rf 



2 



\6e 



1-2 r* 



•4ef 



1-2 € 



l-2r 



3 



20 e 



•9r 



lie 



l*4e# 



1*4 r* 



4 



2-5 e* 



115 r 



1-35 e* 



115 e 



115 r. 



5 



1-65 e 



-6rf 



1-05 e 



10 e 



I0r 



6 



000 



lie 



•85 r 



•55 e 



•9e 



•9r 



•8e* 



•6e* 



l*4e* 



•25 r 



•25 e 



00 



•25 r 



•5e 



•25 e 



'5r% 



•5 e* I 







•4rf 



•25 ef 



•15 rf 



•2rf 



•2ef 



Table II. — Elongations and Retractions in fractions of an inch. 



A. 



B. 



C. 



D. 



E. 



F. 





inch. 



inch. 



inch. 



inch. 



inch. 



1 



•0001375 



0000825 



•000044 



•000077 



•000077 



2 



000176 



•000132 



•000044 



000132 



•000132 



3 



000220 



•000099 



•000121 



•000154 



•000154 



4 



000275 



•0001265 



•0001485 



•000126 



•0001265 



5 



•000181 



•000066 



•0001155 



•000110 



•000110 



6 



000 



•000154 



•0000935 



•0000605 



•000099 



•000099 



•0001168 



•0000876 



•0002044 



•0000365 



•0000365 



00 



•0000365 



•0000730 



•0000365 



■0000730 



•0000730 







•0000584 



•0000365 



•0000219 



0000292 



•0000292 



* Maximum. 



t Minimum. 



