Certain Seasoned Hard Steel Magnets. 



251 





Table II. 



Table III. 



Table IV. 



Results of 25 observations 



Results of 33 observations 



Results of 42 observations 



on a 



seasoned magnet 



on a seasoned magnet 



on a seasoned magnet 



20 cm 



long made of Cres- 



8 cm long 



made of Cres- 



6 cm long made of Cres- 



cent Drill Rod 0-81 cm in 



cent Drill Rod 0-94 cra in 



cent Drill Rod Ml cm in 



diameter. 



diameter 



(Last decimal 



diameter. 



(Last deci- 







place in 



loubt) 



mal place 



in doubt.) 



5 



CS 



& 



a 



Loss of magnetic 

 moment in terms 

 of the moment 

 at 10° C. 



6 

 u 



P 



t 



& 



5 

 u 



Loss of magnetic 

 moment in terms 

 of the moment 

 at 7-6° C. 



i- 



3 



a 

 S 

 85 



Loss of magnetic 

 moment in terms 

 of the moment 

 at 8-1° C. 



10 



o-oooo 



7-6 



o-oooo 



8-1 



o-oooo 



20 



0-0022 



12-0 



0-0033 



12-0 



0-0052 



30 



0-0045 



20-0 



0-0007 



20-0 



0-0160 



40 



0-0068 



30-0 



0-0178 



30-0 



0-0298 



50 



0-0092 



40-0 



0-0262 



40-0 



0-0434 



60 



0-0117 



50-0 



0-0347 



500 



0-0570 



VO 



00142 



60'0 



0-0435 



60-0 



0-0707 



80 



o-oi67 



70-0 



0-0532 



70-0 



0-0845 



90 



0-0194 



80-0 



0-0639 



80-0 



0-0982 



100 



0223 



90-0 



0-0751 



90-0 



0-1122 







100-0 



0-0872 



100-0 



0-1265 



After I had determined the characteristic form of the tem- 

 perature curves of such bar magnets as made up my collection, 

 it remained to find out how the temperature coefficients at 

 ordinary temperatures and the average loss of magnetic 

 moment when the magnets were heated from room temper- 

 ature to 100° C. vary with the dimensions of the magnets. Of 

 course the temperature coefficients of magnets made of dif- 

 ferent kinds of steel may differ widely in absolute value, but 

 my experiments seem to show that for most common kinds of 

 fine steel their values change relatively in much the same way 

 with the dimensions of the magnets. I had a number of 

 brands of steel made by several makers, but the results given 

 here were mostly obtained with Crescent Drill Rod and Jessops 

 Square Tool Steel. Crescent Drill Rod is usually magnetically 

 indistinguishable from Jessops Round Tool Steel. Stubs Drill 

 Rod makes somewhat weaker magnets, but the difference is 

 slight. Some brands of special steel, intended for telephone 

 magnets and the like, make stronger magnets than the polished 

 drill rod, but are not so advantageous as the latter for such pur- 

 poses as deflector magnets, the moments of inertia of which 

 must be computed. The measurements were made in a similar 

 manner to those mentioned in the preceding pages, but the 

 magnet was fixed in a holder in a non-magnetic tube, through 

 which steam, tap water, or water at any convenient tempera- 



