butions from the pen of distinguished writers on commercial 
subjects and applied sciences. It will also be an illustrated 
 cyclopzedia of industrial news, inventions, and improvements, 
collected from Foreign and British sources, for thé use of those 
‘concerned in raw materials, machinery, manufactures, building, 
and decoration. It will carry out what is greatly needed—a 
careful and systematic survey of the industrial activities of 
America, Germany, and France ; in order to present such in- 
formation, as it is useful for British practical men to obtain, at 
the earliest possible moment. Judging from the prospectus it 
seems calculated to serve a very excellent purpose, and we 
heartily wish it abundant success. We have also received the 
first number of a new sixpenny monthly entitled the Workman's 
Magazine, published by Messrs. Kent and Co,, and edited by 
the Rey, Henry Solly, and chiefly devoted to articles connected 
with the social condition of the class whom it addresses. The 
editor, we think, might find a corner for science, the influences 
of which are now felt among all classes. 
Mr. WILLIAM STOKES, JUN., surgeon to the Richmond Hos- 
pital, has been elected to succeed Mr. Hargrave as Professor of 
Surgery to the Royal College of Surgeons, Dublin. 
THE British Medical Fournal understands that the University 
of Dublin, the King and Queen’s College of Physicians, and the 
Royal College of Surgeons, have agreed upon a scheme for a 
joint examining board. The Queen’s University, however, and 
the Apothecaries’ Hall still stand aloof. 
THE Yournal of Horticulture says that a French farmer has 
discovered that the use of tan is an efficient preventive against 
potato disease. For three years he has introduced a small quan- 
tity of the residue of the bark used in tanning into each hole on 
planting his potato crop, and each time he has been completely 
successful in preserving his fields free from the annoying diszase. 
WE have received the catalogue of the mathematical and 
scientific works of the library of the late Mr. Babbage, which 
_are in the hands of Messrs. Sotheby, Wilkinson, and Hodge. 
If not sold by private contract before February 1, 1873, they 
will then be sold by auction. The collection is one of rare 
value, and its dispersion would be an event much to be regretted. 
The catalogue fills 190 pages, and does great credit to the 
compiler. 
THE euilleton of the number for December 28, of the Gazette 
Médicale de Paris, contains the concluding part of M. Dumas’ 
admirable “oge on the late Isidore Geoffroy Saint-Hilaire. 
WE learn from the Zxgineer that Mr, Eden, indoor engineer 
in the Edinburgh Telegraph office, has invented a system by 
which, with the existing instruments, it has been found prac- 
ticable to send messages from both ends of a single wire simul- 
taneously The invention has been tested between Edinburgh 
and Glasgow, and it has been found that one wire is capable of 
doing double work. 
WE learn from Ocean Highways that considerable anxiety 
prevails in Sweden respecting the safety of the vessels attached 
to the expedition which were to have returned at the close of 
the navigable season. The brig G/adan, and steamer Onkel 
Adam, took out stores for the Po/kem, and were to have re- 
turned before the winter set in. They are totally unprepared 
for wintering in the ice; and should they not be able to return, 
it will be necessary for the crews to abandon the vessels and take 
refuge in the Po/kem, which in that case will be overcrowded, 
and crippled in her resources. The Norwegian Government 
has despatched to their relief the seal steamer 4/dert, which will 
make an energetic attempt to reach Spitzbergen. She takes 
out two wooden houses, to erect inshore at the most likely places 
for stragglers to find them, and abundant supplies. 
 NWATURE - 
TERRESTRIAL MAGNETISM * 
L 
[X bringing before you this evening, gentlemen, the subject of 
terrestrial magnetism, it is not my intention to attempt to 
present you with an exhaustive paper on so wide a subject. It 
would be idle to pretend to give in a few short pages an adequate 
idea of all that has been ascertained on this subject, or even to 
present a satisfactory historical sketch of the progress made 
from earliest ages to the present time. Nor will I trouble you 
with a bare enumeration of the many facts, and methods, and 
theories that have gradually led scientific men to their present 
knowledge in this matter. But I will try rather to state, as 
clearly as I am able, what is the actual condition of our know- 
ledge respecting the magnetism of theglobe, and what the nature 
of its complex variations, without, however, entering much into 
details which, though they might perhaps be most convincing 
when reviewed at leisure, ne be entirely out of place here, 
since they would only serve to encumber a paper intended for 
public perusal. 
But, before treating of the special subject of terrestrial mag- 
netism, allow me briefly to recall a few of the well-known pro- 
perties of magnets. 
That certain bodies possess the power of attracting iron was 
not unknown to the most ancient people; and men who had 
noticed this could not long have failed to observe the disturbing 
power that iron, in its turn, exerts upon the magnet when brought 
into its immediate neighbourhood. 
But the duality of the magnetic force was doubtless a dis- 
covery of much more recent times, though now equally familiar 
as the former. That this twofold force ever seeks the opposite 
extremes, or poles, of a magnetic body, and that these poles, 
whilst possessing alike the power of attracting iron, are diametri- 
cally opposed in their action upon the poles of any other magnet, 
is expressed in the trite law that, ‘‘likes repel, and unlikes 
attract.” Again, the law of magnetic intensity was unknown 
until the middle of last century, when it was found by Michell 
to be identical with that of universal gravitation, namely, to 
diminish inyersely as the square of the distance of the body 
attracted, That this was not discovered at an earlier date is 
partly due to the complexity of the phenomena arising from the 
duality of the force, combined with the inseparable nature of the 
two energies. For, unlike electricity, to which in most other 
points it is so near akin, neither the positive nor the negative 
element of magnetism can ever exist alone in any body. 
Now, since we know that magnets and iron act mutually upon 
each other, and that one magnet attracts or repels any other 
according to certain fixed laws, if we remove all disturbing bodies 
from the vicinity of a magnet, and leave it perfectly free to move 
by floating it on a liquid, or suspending it by a thread, we might 
expect to see the magnet remain at rest in whatever position we 
place it. But we perceive at once that this is not the case, and 
the magnet we thought to be free is found to be subject toa 
directive power, which forces it to take a fixed direction, with- 
out in the least interfering with the position of its centre of 
gravity. Disturb the magnet, and when it comes to rest it will 
again lie in the same direction as before. The earth, therefore, 
exerts ajcertain influence on the magnet, not producing any trans- 
lation from one position to another, but only forcing the poles 
of the magnet to assume a definite direction. That this power 
possessed by the earth is precisely similar to that of an ordinary 
magnet, is easily shown by counteracting the earth’s action by 
means of a magnet, placed at a suitable distance from the free mag- 
netic needle, and with its marked end in the same direction as 
that of the needle, the latter will then rest in any position in 
which it is placed. 
This polarity, or directive power of the earth, is said to have 
been known to the Chinese 1,000 years at least before the 
Christian era, ané to have aided them in their long journeys 
across the trackless wastes of their vast empire. The use that 
has since been made of this simple fact, the growth of com- 
merce, the spread of civilisation, and the thousand other bless- 
ings that it has brought to our very doors, need no long comment 
here. We may well marvel that such a source of wealth and 
prosperity was allowed by mankind to remain almost fruitless 
during such a long succession of ages. 
The horizontal direction taken by the freely suspended needle 
*-By the Rev. S. J. Perry, F.R.A.S., F.M.S , Director of the Stonyhurst 
Observatory. Extracted from the ¥ournal of the Liverpool Polytechnic 
Society, by the permission of the Council, Communicated by the author. 
