Nov. 9, 1882 | 
NATURE 
39 
the initial tensions of the wire coils be duly calculated 
and applied © We insist specially on this, because not 
only has the Woolwich practice hitherto been to treat the 
shrinkage question in ahap-hasard rule of thumb method, 
but also Sir William Armstrong, in his late address as 
President of the Institution of Civil Engineers, made 
light of the precise degree of initial tension, and spoke of 
the tendency of the explosive force to effect an adjust- 
ment of the strains. 
We cannot too strongly protest against such a view, as 
crude and unscientific, and any results which may be 
obtained from guns so const:ucted must be inconclusive 
as regards the principle of wire construction. 
In concluding this article we bring before our readers 
sketches of three types of wire guns showing the applica- 
tion of the principle. The first is a heavy muzzle-loading 
gun, designed by the writer for land defences (Figs. 
I and 2). The gun is furnished with rollers on the 
trunnions at G,and recoils upa curved inclined plane, I 11, 
which is mounted on a turnable, so as to be capable of 
training in any direction in azimuth. The elevation is 
given bya hydraulic lift at K. The construction of the 
gun is shown in Fig. 1, in section. AA is the inner tube; 
BB the wire coiled on it; C the breech plug; EE is a 
heavy casting of cast iron, against which the breech plug 
rests, and which also forms the trunnions, GG; KK is a 
cast-iron casing covering the chase of the gun, and 
attached to the casting EE by strong iron bolts, FF. In 
this gun there is no longitudinal strain on the chase; the 
recoil being taken up by the insertion of the heavy mass 
behind the breech plug and by the force of gravity on the 
ascending planes of the carriage, aided by compressors. 
The second type, Fig. 3, is a muzzle-loading gun 
mounted on an ordinary Carriage. The main trunnions 
are behind the breech and are connected to the carriage 
trunnions B by side links C, so that the longitudinal strain 
is transmitted direct from the breech to the carriage with- 
out the intervention of the chase of the gun. 
_ Figs. 4 and 5 represent the type for heavy breech-load- 
ing guns. In this case the breech plug is fixed in a 
massive block, A A, which slides backwards and forwards 
along the side rods, BB. Through this block passes an 
eccentric shaft, C, which terminates on each side in the 
side rods BB. When the eccentric is in its forward posi- 
tion the sliding block closes the breech. Inthe backward 
position the breech is open and the gun tops up on the 
forward trunnions E£, so as to allow of the introduction of 
the charge as shown in Fig. 5. When the charge is in- 
troduced the preponderance is restored to the breech end, 
the gun falls back to its normal position, the eccentric is 
removed, the breech closed, and the gun is ready for 
firing. 
In all these cases it is obvious that there is no longi- 
tudinal strain on the chase of the gun, and it is obvious 
that so far as construction is concerned there is no limit 
to the possible size of the gun. 
James A. LONGRIDGE 
BEN NEVIS OBSERVATORY 
HE conditions of weather on Ben Nevis are now such 
as to render it impracticable and hazardous to con- 
tinue the daily observations satisfactorily. I have there- 
fore judged it best to discontinue them, after a very 
successful season, under the auspices of the Scottish 
Meteorological Society, of five months from June 1, with- 
out the break of a single day. The work at the six 
intermediate fixed stations has, I am very pleased to say, 
been well and generally punctually kept up throughout, 
and I trust that much good will result. Simultaneous 
observations were of course made at the observatory at 
Achintore, Fort William. The Stevenson’s screens at 
these stations have now been made firm by wire 
stays to withstand the storms of winter. Yesterday 
Colin Cameron, the guide, accompanied me. The track 
was snowed up, and it was necessary to force a way 
through great banks and drifts of snow. The average 
depth was two feet ; once we got off our course in the 
blankness of thick cloud-fog and trackless snow. To-day 
the weather was very bad on the summit, the hut was 
partly filled by drift, and the south-east gale was so 
violent at times that I could hardly make way. Possibly 
I shall attempt weekly or periodical ascents during the 
winter to keep up the registrations of the rain-gauges and 
self-recording thermometers. 
I have to-day commenced provisionally a three-hourly 
system of observation at Fort William (including 3 a.m.). 
The special features are sea temperature, ozone, and the 
reading and setting of the self-registering instruments on 
each occasion. Of course all the other usual elements 
are three-hourly observed also. Further particulars are 
reserved for a future number. CLEMENT R. WRAGGE 
Fort William, November 1 
THE OYSTER INDUSTRY OF THE UNITED 
STATES 
A VERY complete account of the history and present 
condition of the oyster industry of the United 
States has been recently prepared by Ernest Ingersoll, 
under the direction of Prof. Baird, United States Com- 
missioner of Fisheries. The importance of this industry 
it is not easy to over-estimate, and the United States 
Government deserve every credit for their efforts to pre- 
serve and extend it. 
As having an important bearing on the question, the 
oyster-beds of the maritime provinces of Canada are 
briefly referred to. The eastern coast of the province of 
New Brunswick is washed by the Gulf of St. Lawrence ; 
down in the bottom of the Gulf lies the long, irregularly 
shaped Prince Edward’s Island, between which and the 
mainland flow the shallow but troublesome currents of 
Northumberland Strait. The shores on either side of this 
Strait are for the most part low bluffs of reddish soil and 
sloping meadows ; there is little solid rock, few prominent 
headlands, but a continuous line of shore, shelving very 
gradually into water, nowhere deep; many rivers come 
down along the coast of the Gulf, and at the mouth of 
each there is an estuary proportionate to the size of the 
stream, from the mighty channel of the St. Lawrence to 
the miniature bay of Bedeque. Most of these estuaries 
are shallow, and most of them are protected from 
gales. This condition of affairs seems well suited for 
oyster growth, since nearly all of these estuaries either 
contain or contained large colonies of these mollusks. 
Except at its western end, Prince Edward Island is 
engirdled with oysters. That most beautiful salt-water 
lake in the world, the Bras d’Or, which occupies the 
whole interior of Cape Breton Island, fattens multitudes 
of oysters. These Canadian oysters are of large size, and 
have thick, strong shells; oysters with shells trom eight 
to ten inches in length are not extraordinary. The best 
are not the longest, but those with straight and narrow, or 
evenly-rounded shells. All the oysters on the eastern 
shores of North America, belong to the species known as 
Ostrea virginiana, which embraces many varieties, of 
which O. dorealis is perhaps the best marked. Except at 
wholly unsuitable places, it is to be found almost without 
interruption from the northern shores of the Gulf of 
Mexico and the coast of Florida to the Canadian districts 
just referred to. It is, however, said not to be found 
along the eastern shores of Maine, nor in the Bay of 
Fundy, though the shells, in a semi-fossil state, are dug 
up in quantities from the deep mud in the harbour of 
Portland, Maine. 
Mr. Ingersoll gives a very interesting account of the 
former extent and condition of the native beds in the 
Gulf of Maine, and of the evidence of the immense con- 
