Chemistry and Physves. 3809 
of Science; letter dated Dublin, March 1, 1887.—In Messrs. Barus 
and Strouhal’s paper on the Viscosity of Steel, published in the 
January number of your Journal, the authors refer (p. 35) to the 
various physical changes which steel undergoes at a certain criti- 
cal temperature. They do not seem to be aware of the investiga- 
tions I have published on the ‘‘ Molecular changes that accom- 
pany the Maenetization of Iron and Steel,” for they refer to 
“Baur” (Wied. Ann., 1880) the disappearance of the magnetic 
state at the critical temperature. ‘This fact they will find noticed 
in the report of a lecture of mine at the London Institution on 
April 23, 1873, published in the Journal of that institution in 
July, 1873; it was also mentioned in my papers in the Philo- 
sophical Magazine for December, 1873, and January, 1874. 
Messrs. Barus and Strouhal appear also to have overlooked the 
curious “ after-glow” in steel wire, a discovery I made in Septem- 
ber, 1873, and published in the Philosophical Magazine for 
December of that year. Perhaps you will allow me to state the 
main points in that.paper, which are as follows: 1. Mr. Gore, in 
1869, had discovered that a momentary elongation of iron 
occurred in cooling after heating a wire of that metal to a white 
heat. In 1872 I found a similar but reverse action took place 
in heating the wire. 2. This anomalous deportment was found 
both in heating and cooling to coincide with, on the one hand the 
Joss, and on the other with the resumption of the magnetic state 
of iron or steel. 3. At the critical temperature the wire, having 
cooled down to a dull red heat, suddenly flashed into a bright 
glow; likewise during the heating of the wire the temperature 
remains stationary for a short time when the critical temperature. 
is reached ; a rise in the specific heat of wire and steel therefore 
occurs at the critical temperature. 4. A curious crepitation 
occurs at the critical temperature, similar to that heard in the 
magnetization of iron, or in the production of the scales of oxide 
on the wire. 5. Thermo-electric inversion occurs at this same 
temperature. 6. Hard iron wire and steel wire exhibit the 
phenomena but certain specimens of good soft iron failed to show 
it, and even in the wires that exhibit it the phenomenon grows less 
marked after repeated heating and cooling and finally disappear. 
To these observations I may add that a recent investigation on 
the properties of manganese steel wire (Proc. Royal Dublin 
Society, December, 1886) shows that this body, which is almost a 
non-magnetic metal,* does not exhibit the anomalous deport- 
ment observed in ordinary steel wire. ‘This fact is of considerable 
interest as linking the foregoing phenomena more closely with 
the magnetic state of iron and steel. 
In conclusion, permit me to thank Messrs. Barus and Strouhal 
for their very carefully conducted and admirably devised series 
* Tn the paper referred to I have shown that if the magnetic susceptibility of 
iron be 100,000, that of manganese steel is only 300, about the same as ferric 
oxide. 
