JUNE 22, 1899] 
LETTERS TO THE EDITOR. 
(The Editor does not hold himself responsible for opinions ex- 
pressed by hits correspondents. Netther can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NATURE. 
No notice ts taken of anonymous communications. | 
The Magnetic Compass and Nickel Cases. 
Ir is a common practice arnongst instrument makers to put the 
magnetic compass needle of the pocket compass, or the marching 
compass used in the army, into an external case of nickel ; the 
case is usually furnished with a lid, after the manner of a hunting 
watch, and is largely used by travellers. 
Recently, while in South Australia, I used such a compass, 
which was lent to me, for the purpose of steering across a rather 
large ‘‘run.” On comparing my position with that indicated by 
the map, I found that I had drifted considerably to the right of 
the point laid down; on examining the compass, while slowly 
shutting the lid, I noticed that as it closed the card of the com- 
pass was deflected. I next noticed that the case, which was 
much discoloured, and at first sight looked like bronze, was 
made of nickel; this revealed the source of error—when the lid 
was open, the nickel case, which is magnetic, was unsymmetrical 
with respect to the magnetic needle, and the needle was 
attracted by the lid from the true magnetic meridian, and the 
compass thereby rendered useless for steering purposes, and a 
source of possible danger, when long distances are traversed. 
On talking over the matter with a leading instrument maker, 
I found that nickel is usually supposed to be.a non-magnetic 
metal, and that nearly every traveller’s compass case is made of 
nickel. It is somewhat remarkable, in an age of so many 
technical schools, that such ignorance can exist about a metal 
the properties of which were spoken of by Faraday in 1845 thus : 
“<The magnetic characters of iron, nickel and cobalt are well 
known” (Phil. Traus., 1846, p. 41). On looking through 
different price lists of leading firms selling marine compasses, I 
find that nickel enters into their construction also. In marine 
compasses the presence of a magnetic metal in the cases must be 
a source of some danger to the navigator. I would suggest 
that when selecting a magnetic compass, the magnet needle 
should be removed, and the case carefully tested for magnetic 
properties, and that should the case show any signs of magnetism 
it should be rejected. F, J. JERVIS-SMITH. 
Oxford, June 13. 
Historical Note on Recalescence. 
In his recent presidential address to the Iron and Steel 
Institute, Prof. Sir W. Roberts-Austen stated (NATURE, No. 
1541, p- 43) : ‘‘ To Gore, and to Barrett, we owe the investigation 
of the nature of a fact which had long been well known to 
smiths, that iron on cooling from a bright red heat suddenly 
emits a glow.” 
I do not know what authority Sir W. Roberts-Austen has for 
this statement, but as this is not the first time it has been made, 
perhaps I may be allowed to ask if he has any documentary 
evidence in support of it. So far as I am aware the history of 
the matter is as follows :—At the meeting of the British Asso- 
ciation in Bradford in September 1873, I read a paper entitled 
“On certain remarkable molecular changes occurring in iron 
wire at a low red heat”’ ; this was subsequently published in the 
Philosophical Magazine for December 1873. In this paper, 
the phenomenon, for which I suggested the name recalescence, 
was first described, and was further investigated in other papers 
of mine, to which I need not here refer. At the time of the 
discovery it seemed to me highly probable that this remarkable 
after-glow in cooling iron and steel was likely to have been 
already noticed, but after considerable search I could find no 
previous record of it in scientific literature; nor could I, after 
persistent inquiry, discover a single smith or iron-master who 
had even casually noticed the effect until I pointed it out to 
them. . 
But the most curious thing was that the observation had 
entirely escaped Dr. Gore’s attention ; in 1869, Gore discovered 
that a momentary elongation occurred in a cooling iron wire 
after it had been heated to bright redness. Dr, Gore, how- 
ever, did not pursue the matter further, and informed me in 
May 1872 that he had no intention of doing so (see Phz/. Mag., 
December 1873, p. 473). Writing ‘to me, after the publication 
NO. 1547, VOL. 60] 
NATURE 
E73 
of my paper in 1873, in a letter which I happen to have kept, 
Mr. Gore says :— 
“Edgbaston, Birmingham, December 2, 1873. Your new 
discoveries respecting the molecular changes in iron, described 
in the Phz/. Mag. for this month, have greatly pleased me ; 
especially the sudden development of heat attending the 
elongation during cooling, and the sudden shortening during 
heating. . . .”! And ina letter to me some years later—after 
the delivery by Prof. Roberts-Austen of a lecture before the 
British Association in 1889—Dr. Gore naturally expressed his 
surprise that the discovery or investigation of recalescence 
should be attributed to him. 
It is to M. Osmond more than any one else we owe the 
series of masterly investigations that has raised the discovery 
of recalescence into the importance which it now holds in the 
metallurgy of steel. The value of M. Osmond’s work is 
well known, but I am glad of this opportunity of emphasising 
it, for M. Osmond’s modesty has led him to attribute in his 
papers, and in his correspondence with me, more value to my 
own work than it probably deserves. For instance, in a letter 
addressed to me from Paris on December 13, 1889, M. Osmond 
writes :—‘‘ Vos observations sur la Recalescence sont de celles 
qui feront époque dans Vhistoire de la métallurgie ; elles ont 
eté le point de départ de tout ce qu’on a fait pendant ces 
derniéres années, et pour mon compte, j’ai tant travaillé sur vos 
traces qu'il me semble vous connaitre depuis longtemps. . . .” 
I feel sure my friend Sir W. Roberts-Austen will forgive 
my venturing to correct him in this trifling matter of scientific 
history. It is quite possible his statement, that recalescence 
‘had long been well known to smiths” prior to 1873, may 
be derived from his wide metallurgical knowledge, which I do 
not presume to possess, or it may arise from the common and 
unintentional blunder of reading our present knowledge into the 
ast. W. F. BARRETT. 
Royal College of Science, Dublin, June 2. } 
IN the Presidential address referred to, I attempted to review 
the progress made in connection with iron and steel during the 
past century. [ felt that, notwithstanding the very limited space 
at my disposal for recording the work of individuals, the name of 
Barrett must find a place, and I greatly regret that my friend 
considers the reference to him to be infelicitous. As regards the 
first point raised by him (to take the class of smith’s work with 
which I have most experience), those who have to conduct the 
very delicate operation of hardening dies for coinage have long 
been familiar with what is now known, thanks to Prof. Barrett, 
as ‘‘recalescence” in cooling steel. Of course the artificers 
were ignorant of its true cause, and they usually describe the 
effect of the sudden glow in steel as being due to “‘ the heat 
coming from inside the metal.” The fact that this industrial 
knowledge existed, doesnot in the least diminish the interest 
of Prof. Barrett’s own observation (1873), nor lessen the vital 
importance of his work in showing that ‘‘ Gore’s phenomenon” 
(1869) is a reversible one. The relation of the work of Barrett 
to that of Gore was, moreover, indicated by me nearly ten 
years ago in the pages of NATURE (November 7, 1889, p. 16) 
as concisely as I could. In a recent number of NATURE 
(April 13, 1899, p- 567), a curve obtained by a method of my 
own is published, and it shows that there are no less than six 
points at which heat is evolved as iron cools down from 1150° C. 
to the ordinary temperature. I wish that Prof. Barrett, with 
his great experimental skill, had hastened the advance of our 
knowledge by continuing, during the past twenty-five years, in- 
vestigations which would have led him to the discovery of the 
several very important points in carburised iron in which, as the 
1 In a note to the Iron and Steel Institute in 1890, and in correspondence 
with me subsequently, Dr. Gore points out that the discovery of the 
“Sudden shortening during heating” he here attributes to me 1s more or 
less implied in his own paper in the P#z/. Mag. for September 1870, where 
a molecular change occurring in iron during the process of heating is 
clearly mentioned. But the only evidence Gore gives of a molecular change 
during the Aeating of iron is the production of an induced current in a 
surrounding coil of wire when the iron core reaches a certain temperature ; 
this he correctly attributes to the well-known change in the magnetic state 
of iron at this temperature. In fact, quoting from his previous paper, Dr. 
Gore states (the italics are his): ‘‘ The iron during cooling . . . suddenly 
elongated by diminution of cohesion . . . a corresponding but reverse 
phenomenon did of occur during the process of Aeating the wire” (Phil. 
Mag., September 1870, p. 171). In an interesting research on ‘The 
changes in length and temperature of iron and steel during recalescence,” 
published in the PAzl. Mag. for August 1898, M. Svedelius of Upsala 
supports the historical view I have here taken. 
