Jury 8, 1915| 

doubt that the protective use of tetanus antitoxin is 
the principal cause of the disappearance of tetanus 
among our wounded; there are but very few cases of 
it now. Sir William Osler, at the annual meeting 
of the Research Defence Society on June 30, rightly 
emphasised this point; it does not need to be em- 
phasised for those of our readers who are medical 
men and have watched cases of tetanus. 
After the meeting Dr. Andrew Balfour gave a 
demonstration of the protective treatment against 
typhoid, showing, with-admirable ingenuity, how com- 
pletely the resistance of the body to invading germs 
may be described in terms of human warfare. Not 
all men of science are skilful in the use of parables, 
but he is. 
Some day, those of us who live long enough will be 
able to read the medical and surgical history of the 
present war. It has been taken in hand by many 
writers of authority, and it will be fine reading. It 
will interpret to us one of the noblest records of science 
in practice. Interpreters of science, popularisers of 
science, are always useful, and the Research Defence 
Society has certainly done useful work by interpreting 
and popularising the methods and the achievements 
of modern physiology and pathology. 

FERROMAGNETISM AND THE 
TRANSFORMATION IN IRON. 
|e years have witnessed a remarkable con- 
centration of experimental research on the critical 
point Az in iron. Moreover, whereas up to the year 
1904 investigations of this character were carried out 
chiefly by metallurgists and engineers, since that date 
there has been a most welcome entry of physicists and 
physical chemists into this field of research, who in 
virtue of their different training and outlook have 
investigated the problem from a somewhat different 
point of view, and, it must be granted, by more 
rigorously scientific methods. The paper by Mr. 
Kotaro Honda, of the Imperial Tohoku University, 
Japan, on the nature of the A2 transformation in iron, 
presented at the spring meeting of the Iron and Steel 
Institute in London, is a valuable contribution by a 
physicist who has made a special study of this ques- 
tion for a number of years. 
Broadly speaking, there are three views of the 
nature of the A2 transformation which the author 
summarises in the following language :— 
“(7) The transformation is an allotropic change 
(a to 8) occurring at a definite temperature, or at 
least within a small range of temperature; (2) f-iron 
is not an independent phase but a solid solution of a 
and y iron; (3) the transformation is not an allotropic 
change but an intermolecular change taking place in 
the a phase within a considerable range of tempera- 
ture.” 
The first view is historically the oldest, and is par- 
ticularly identified with the late M. Osmond. It was 
warmly adopted by Roberts-Austen and his co-workers, 
and is apparently still supported by Tammann, Howe, 
Sauveur, Burgess, and Rosenhain, although it raises 
several difficulties in explaining the facts actually 
observed. The second view was enunciated in 1912 
by Benedicks, but although at first sight a promising 
case was made out, and it appeared to be supported 
by atest research published by Carpenter in 1913, it is 
in conflict with many well-established facts, and has 
been practically abandoned. The view that A2 is not 
an allotropic or phase change was first put forward 
by H. Le Chatelier, and shortly afterwards by P. 
Weiss. It numbers among its additional supporters 
at the present time Benedicks, Hadfield, Carpenter, 
Edwards, McCance, and Honda. It is the most 
modern view of the nature of the transformation. 
NO. 2384, VOL. 95] 
A2 
NATURE 
379 
Mr. Honda’s experimental contributions to the study 
of the nature of the Az critical point as revealed in 
his paper relate to (1) the thermal changes associated 
with the transformation; (2) magnetisation at high 
temperatures; and (3) magnetic expansions at high 
temperatures. With respect to the first-named they 
confirm what has long been known, viz., that the 
heat evolution on cooling, and heat absorption on 
heating corresponding to the Az transformation take 
place over a wide range of temperature, at least 100° Cr 
although the greater part is evolved or absorbed within 
30-40° C. The complete range, however, is probably 
considerably more than 100° C. <A transformation 
extending over so wide an interval cannot properly 
be regarded as an instance of ‘one-phase allotropy.” 
Neither is it correct to speak as Burgess and Crowe 
do of the temperature at which dq/d6@ is a maximum, 
as the critical point or range. The author regards the 
temperature at which the heat evolution begins on 
cooling, or the heat absorption ends on heating, as the 
critical point, and uses the expression in this sense. 
It is also the temperature at which ferromagnetic 
iron becomes paramagnetic, or vice versa. 
The most important section of Honda’s paper is 
that dealing with magnetisation at high temperatures. 
Many metallurgists hold the view that the magnetisa- 
tion of ferromagnetic metals undergoes an abrupt 
change at their critical points, but this is seldom 
the case. In fact, the course of the temperature- 
magnetisation curves changes markedly with changes 
of strength in the magnetising field, and Honda’s 
experiments on pure iron, nickel, and various kinds 
of steels show this clearly. In a very weak field the 
magnetisation of iron and nickel increases with tem- 
perature at first slowly, and then very rapidly, and 
after reaching a sharp maximum it falls extremely 
quickly at the critical temperature. If the strength of 
the magnetising field is augmented this effect of in- 
creasing magnetisation becomes continually less. In 
a field of several gauss the magnetisation remains 
constant up to the critical point and then falls very 
rapidly. With further increase of field the magnetisa- 
tion begins gradually to decrease from a temperature 
which is lower as the field is stronger, and in a field 
of several hundreds the magnetisation begins gradually 
to decrease from the room temperature. In all cases 
the effect of temperature on magnetisation is_ two- 
fold, and the observed change of magnetisation is the 
sum of these two effects. The first effect is specially 
conspicuous in weak fields, and becomes continually 
less as the field is increased. It is similar to the well- 
known mechanical tapping on magnetisation, which it 
increases, the thermal agitation playing the part of 
mechanical shocks. The second is a reversible effect, 
and always acts in diminishing magnetisation. By 
incessant thermal impacts the molecular magnets 
execute rotational vibrations about their mean orienta- 
tions, and the mean magnetic effect is diminished by 
the vibration. It is easy to see therefore that the 
decrease of magnetisation increases with the amplitude 
of rotational vibration—i.e. with rise of temperature. 
In very strong fields the first effect no longer obtains 
and there exists chiefly the second reversible effect of 
temperature. ; 
Mr. Honda has concerned himself only with the 
latter, which is much the more important of the two. 
With respect to iron, his conclusion is as follows :— 
“Tn strong fields when the irreversible thermal effect: 
is negligible the magnetisation begins to diminish 
from the lowest temperature, the change per degree 
of temperature increasing at first gradually but becom- 
ing always greater as the critical temperature is 
approached. If the change of magnetisation indicates 
that an intermolecular change is taking place in the 
| substance which at the same time manifests itself 

