338 B. 0. Peirce — Properties of Seasoned Magnets. 



about three times as great at 100° C. as at the temperature of the 

 tap water. 



Tables III, IT, and V show the results of a large number of 

 measurements on magnets made of two well known brands of 

 self-hardening steel. If the lengths of the magnets are used 

 as abscissas and the corresponding numbers in the last two 

 columns of each of these tables as ordinates, we get the curves 

 represented in figures 4, 5, and 6. In the case of magnets 

 made of ordinary fine tool steel, the differences between the 

 temperature coefficients at low temperatures and at the temper- 

 ature of boiling water, which are large when the magnets are 







i 



0.075 





1 



0.050 







0.025 



/ 2 



5 5 



75 



short, often become insignificant when they are relatively 

 long. No such tendency is shown in the curves here printed. 

 A 'portion of the upper curve in figure 6 which seems too 

 nearly vertical, was drawn through points obtained by measur- 

 ing a large number of magnets less than 4 cm long. 



The work of Mr. Durward appears to show that whereas rela- 

 tively long magnets made of fine tool steel generally have 

 smaller temperature coefficients than relatively short ones, we 

 cannot hope to reduce to zero the temperature coefficient of a 

 magnet made of stout rod by lengthening it indefinitely. It 



