186 Prof. A. M. Mayer on the Magnetic Elongations 



to the heat produced in the rod at the instant of its demagneti- 

 zation. Tt is also noteworthy that, from the moment of break- 

 ing the circuit in an experiment until the forming of it in the 

 succeeding one, the scale remained immovable. Taking 1'2 

 division as the amount of elongation and retraction due alone to 

 magnetization and demagnetization, we can determine the mean 

 amount of elongation at the moment of demagnetization as fol- 

 lows. The mean elongation in experiments 6 to 17 is 1*18 di- 

 vision. This is only *02 of a division less than 1*2, and can 

 candidly be attributed to the errors of observation ; but the mean 

 retraction of the same experiments is 1*08 division, which is 

 •12 of a division less than 1*2, and gives us the measure of the 

 effect due to the heating of the rod at the moment of its demag- 

 netization ; for on keeping the rod at the temperature it had 

 during experiments 1 to 5, we found that it gradually retracted 

 until the scale again remained steady at 38'0. 



Table II. is here given to show that nearly the same effects of 

 elongation and retraction are observed when the rod is gradually 

 elongating under the effects of heat radiated from the helix, 

 when the latter has a powerful current passed through it. 



Table II. 



No. of 

 experiment. 



Scale, 



Scale, on 



Scale, on 







circuit 

 open. 



closing 



circuit. 



breaking 

 circuit. 



Elongation 



Retraction. 



18. 



514 



528 



51-8 



14 



10 



19. 



51 8 



53-2 



522 



14 



10 



20. 



522 



534 



524 



12 



10 



21. 



52-5 



538 



52-7 



1-3 



11 



22. 



52-8 



540 



52-9 



12 



1-1 



23. 



530 



543 



53-2 



13 



11 



24. 



53-2 



545 



53-5 



13 



10 



25. 



535 



547 



53-6 



12 



11 



26. 



538 



55-2 



54-2 



1-4 



10 



27. 



54-2 



554 



54-4 



1-2 



10 



28. 



54-4 



55-6 



54-5 



1-2 



11 



29. 



54-5 



557 



547 



1-2 



10 



30. 



54-8 



55-8 



5475 



1-0 



105 



31. 



54-8 



56-0 



55 



12 



10 



32. 



550 



56-2 



55 2 



12 



10 



33. 



552 



56-3 



55-25 



11 



105 



34. 



55-25 



56-4 



55 4 



115 



10 



35. 



55-4 



56-45 



55-5 



105 



0-95 



The experiments in the above Table were made on the same 

 rod used in the experiments in Table I.; but before this new 

 series was commenced I passed round the helix a stronger cur- 

 rent than previously used, so that the rod was elongated by the 

 heated helix from 39*2 divisions of the scale to 51*4 divisions; 

 and while the scale was advancing to this reading, I determined 



