176 A. M. Mayer — Effects of Magnetization 
constituent particles of the magnet as the cause of the pheno- 
mena. On the other hand, the fact that the shortening effect is 
proportional to the magnetic intensity of the bar multiplied by 
the current traversing the coil, seems to indicate that, in this 
case, the effect is produced by the attraction of the magnetic 
particles by the coil. But then it will be asked, why so remark- 
able an augmentation of the effect is produced by the increase 
of tension in the case of the soft iron bars hen we are able 
to answer this question in a satisfactory manner, we shall prob- 
ably have a much more complete acquaintance with the real 
nature of magnetism than we at present possess.” 
This full account of Dr. Joule’s remarkable research is here 
presented in order to give an exposition of our present knowl- 
edge of this subject, and clearly to set forth the relations which 
my own attempts bear to his labors) Here Joule, the dis- 
coverer of these phenomena, has given us almost all the knowl- 
ge we have, up to this time, possessed in reference to their 
characteristics and their laws. That a subject so fascmating 
should not have been eagerly followed up appears strange ; 
especially so, when it seems highly probable that the faithful 
study of these actions may one day give us an insight into the 
dynamic nature of electro-magnetization and thus lead the 
investigator into a fruitful field of research. : 
No one can duly appreciate this work of Joule’s until he 
attempts the confirmation of his results; then the difficulties of 
the research and the skill and acumen of this eminent physicist 
will be properly estimated. 
Ithough the cognate discovery by our countryman Page, 
in 1837, that iron bars produce sound on their magnetization, 
has been carefully studied by Delezenne, De la Rive, Beatson, 
Marrian, an ertheim, yet in the annals of science I have 
found only two experimental investigations, in addition to the 
one by Joule, on the phenomena of the elongation produced 12 
iron rods on their magnetization. The first is by Wertheim, in 
the Ann. de Ch. et de Phys., 3¢ Serie, t. xxiii; the second by 
Tyndall, contained in a paper entitled “On some Mechanic 
Effects of Magnetization ;” published in his ‘‘ Researches on Dia- 
magnetism and Magne-Crystallic Action,” London, 1870. 
In Wertheim’s memoir “ On the sounds produced in Magne- 
tized Iron,” all we find on the subject of the elongation of 
magnetized iron rods is the following: ‘Here are the results 
of these experiments: the helix being placed so that its axis 
coincides with that of the bar, we do not observe any lateral 
movement, but only a very small elongation; this elongation 
rarel — ‘002 millimeter, [in rods about 970 millimeters 
eter and although visible is bearly measurable; it is most 
pronounced when the helix [whose length was a little over 3th 
