Nov. 9, 1882] 
DATE 
anc 
rope) 
The object of performing the experiments with several 
_magnets, is to eliminate as far as possible, errors in the 
determination of weight and length. The mean of the 
values of H, found for the several magnets, is to be taken 
as the value of # at the place of the magnetometer. We 
have now to apply this value to the measurement of 
currents. ANDREW GRAY 
(To be continued.) 
THE ITALIAN EXPLORATION OF THE 
MEDITERRANEAN 
BELIEVE it will interest the numerous readers of 
NATURE, especially those who have studied the 
important subject of the deep-sea fauna, or who are 
geologists, to learn that the further exploration of the 
Mediterranean this year, on the part of the Italian 
Government, has not been fruitless, although it has been 
short. I have just received a letter from Prof. Giglioli, 
of Florence, the purport of which I will, with his permis- 
sion, now give :— 
It seems that this summer the surveying-vessel, Wash- 
tngtow, had to undertake a search (which proved unsuc- 
cessful) for some imaginary coral-banks in the shallow 
sea between Sicily and Africa, besides her usual hydro- 
graphical work, and that consequently very little time 
could be devoted to deep-sea exploration. However, 
Prof. Giglioli was allowed to accompany the hydrographer, 
Capt. Magnaghi, with the chance of taking any favourable 
opportunity that might occur. He thus got three deep- 
sea hauls: the first near Marittimo, in 718 metres, or 
about 389 fathoms ; the second, half-way between Sicily 
and Sardinia (lat. 38° 38’ N., long. 10° go’ E.), at a depth 
of 1583 metres, or about 857 fathoms, when a very rare 
and peculiar abyssal fish (Paralepis cuviert), was obtained. 
That day (August 15) was also appropriated to hydro- 
graphical researches, and particularly to the successful 
trial of Capt. Magnaghi’s new water-bottle, as well as to 
the marvellous work of his new currentometer, a most 
valuable discovery, by means of which the direction and 
force of sub-marine currents can be accurately determined 
at any depth. A large new trawl was used, and brought 
up a block of newly-formed limestone, which had been 
hardened with recent shells of Pteropods embedded in 
its mass. The third and last deep-sea dredging was 
made on September 1, between Tavolara in Sardinia, 
and Montecristo, in 904 metres, or about 490 fathoms, 
with indifferent results. He will send me the shells for 
examination. The Italian Ministry have promised him 
that a whole month next year will be allowed for deep- 
sea exploration. J. CWyYN JEFFREYS 
WIRE GUNS} 
Il. 
iz has been necessary to dwell thus at length on the 
hoop method of construction in order to contrast it 
with the wire system, which we now proceed to describe. 
A wire gun consists first of an internal tube, the function 
of which is to contain the rifling, and to transmit the 
internal pressure to the wire which is coiled upon it, and 
which gives the strength. This tube no doubt has a 
certain amount of strength of its own, but this is not its 
real function. The gun may be so designed and con- 
structed that the tube is never in a state of tension. It | 
may therefore be made, and possibly with advantage, of 
hard cast iron. In the 3 inch breech-loading gun made 
by the writer in 1860, the tube was of cast-iron } inch 
thick, and this gun has been severely tested without 
injury. Hard cast-iron possesses many advantages, and 
amongst others that of great economy as compared with 
the steel tubes now generally used ; but whatever be the 
* Continued from p. 14 
material of the tube, its principal function is to contain 
the rifling and transmit the strain to the wires coiled 
around it. 
Upon the inner tube is wound steel wire, square or 
rectangular in section. The tube is mounted in a machine 
similar to a lathe, and the wire is coiled upon one or more 
cylindrical drums, which are fixed horizontally on axes 
parallel to the tube and provided with proper apparatus 
tor regulating the feed andtension. The tensions having 
been first calculated, the coiling begins from the breech- 
end where the end of the wire is made fast. When the 
muzzle end is reached the wire is coiled back again to the 
breech, and this process goes on till the whole of the coils 
are in place. The end of the wire is then made fast, and 
the gun, so far as strength to resist a bursting strain, 
which is called circumferential strength, is concerned, is 
complete. 
Before proceeding to show how the longitudinal strength 
is provided for, it will be well to devote a little time to 
the substitution of coils of wire for the hoops above 
described, pointing out as we go along the superiority of 
the wire system. It has already been shown how im- 
portant it is in the hoop system that the initial tensions 
20 TONS PER SQ.INCH. TENTION, 
F 
6 INCHES. 
of each hoop should be accurately calculated and applied. 
This is no less necessary with the wire coils, and it would 
at first appear that this must involve very intricate and 
tedious calculation. In the case of the gun represented 
in Diagram C, it was stated that the same strength which 
was given by 4 coils of steel, making with the tube a total 
thickness of 22} inches, might be obtained by 63 inches 
of wire, but supposing the wire to be ,/5th inch square in 
section there would be required no less than 67 differen: 
coils and tensions, and as it is desirable to use even smaller 
wire for the first portion of the cc ils, there would probably 
be not less than 80 or go coils and the same number of 
tensions to be calculated. A formula has, however, been 
found which makes these calculations comparatively 
simple. In order to make this intelligible we must resort 
to another diagram, E, which represents the state of 
strain of the interior of a wire gun, or rather of the wire 
portion of it, on which alone we depend for circumferential 
strength. Assuming the wire to be very small, say jth 
of an inch square in section, the strains are represented 
very nearly by the curved line BNM. The coils between 
the inner circumference, z.¢ the first coil, and the point N 
are all in compression, the maximum being at C; at N is 
the neutral point, when the wire is neither in compression 
nor tension ; and from N to F all the coils are in tension, 
the maximum being at F. ; 
