514 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Low Carbon Steel . — A similar examination of a specimen of the low 
carbon steel showed that similar turning points occur in the susceptibility- 
temperature curve. They are, however, much less marked than those 
contained in the corresponding curves for the steels containing higher 
percentages of carbon. 
Soft Iron. — The susceptibility - temperature curves yielded by a 
specimen of soft iron were entirely normal. There is no indication of 
a set-back in the susceptibility until the temperature approaches the 
critical temperature. 
In the following table the most important of the preceding results are 
collected together for the sake of comparison, and it may be observed at 
this point that these results refer only to values of the magnetising force 
exceeding 2 c.g.s. units, and are therefore not necessarily true for very low 
fields. As a matter of fact, the lower the value of the magnetising force 
the less marked is the first transformation point, as has already been 
pointed out. In the table, T x is the temperature at which the first 
maximum appears in the susceptibility-temperature curve, and T 2 is the 
temperature at which the first minimum appears. 
Table II. 
Yariety of Steel. 
Percentage of 
Carbon. 
T t . 
t 2 . 
Cast iron 
3T5 
180° C.-200 0 C. 
240° C.-270 0 C. 
High carbon . 
P64 
210° C.-230 0 C. 
250° C.-270 0 C. 
Medium carbon 
0-8 
180° C. 
220° C. 
Low carbon 
0-3 
110° C. 
140° C. 
Soft iron 
0 06 
Comparing first the temperatures of minimum susceptibility we see that 
while that for cast iron and that fox* high carbon steel are almost the same, 
that for medium carbon steel is lower than for either of the specimens 
containing a high percentage of carbon ; that for low carbon steel is lower 
still. Also the range of temperature within which the bend takes place 
tends to become smaller as the percentage of carbon diminishes. Again, 
the magnitude of the set-back in magnetic quality in the neighbourhood 
of 200° C. becomes less marked with diminishing quantity of carbon. 
When the percentage of carbon is as low as 0‘06 per cent, the set-back is 
no longer perceptible. 
In conclusion, it may be remarked that the writer has failed to detect 
any indication of the presence of a transformation point for steel in the 
neighbourhood of 200° C. in the curves obtained by previous workers in 
