150 
MINUTES OF PROCEEDINGS OP 
much as iron across the fibre is only half as strong as it is along the 
fibre. The breech-piece, also, is very thick, and undergoes a still 
further loss of strength on that account. Altogether, we can only 
count on one-half of the tension of bar iron for the inside of the breech- 
piece, and something like one-sixth or one-eighth for the outside, and 
on a total strength of not much more than one-fourth of the useful 
effect of the iron. In Fig. 3 , the shaded portion of the diagram shows 
how much strength is lost. 
When we come to the outside coils, the conditions are apparently 
much more favourable, for there seems to be very little strength lost. 
But these coils are far removed from the bore, and, as we have seen, 
there is not the same certainty of their doing their work as there would 
be if they were near. Also, since the bursting of the 600 -pr., the 
initial tension has been very much reduced, and the same amount is 
not now given, as shown in the diagram. Owing to the large diameter 
of these coils, they are expensive to make, so that this is not an 
economical way of getting up the strength. 
Another fault may be added. The longitudinal strain is, to a con¬ 
siderable extent, borne by the steel barrel, contrary to Major Palliser's 
principle and Mr. Bigg's objection to the cross strain on the bore. It 
is, however, to be remembered that, at Elswick, these guns were first 
made with a loose end, which avoided the cross strain on the bore, and 
threw all the longitudinal strain on the breech-piece. The advantage 
thus gained is, however, very questionable ; for if the longitudinal strain 
be not partly borne by the steel tube, it is necessary to have a thicker 
breech-piece, which leads to even greater errors, as we have seen. 
None of these guns are now made with loose ends, but they are some¬ 
times made at Elswick with thinner breech-pieces. 
3. Fraser Guns. 
a. With one Triple External Coil. 
Fig. 12 shows the first pattern that was made without a longitudinal 
breech-piece. So far, this is a very important step; for if the gun be 
all coiled iron, it will much better resist the most dangerous circum¬ 
ferential strain. In the construction of this gun there has evidently 
been a due regard paid to longitudinal strain, as well as to economy; 
for there is a good thick steel tube, as well as a very thick coil, brought 
to bear on it. If the thick coil be properly welded, the longitudinal 
strain may be fairly considered as met. 
But mark the other objections which this involves. Owing to the 
great thickness of the external coil, j- of its useful effect only can be 
obtained for circumferential strength, seeing that the internal and 
external diameters are as 2 to 5 . Also, on the one hand, if the welds 
are not properly made, there will be a deficiency of longitudinal 
strength; and, on the other, if to make sure of longitudinal strength 
the iron be strongly heated, there is a danger of the iron becoming 
deteriorated by overheating. These are the two dangers which have 
to be avoided in manufacture; and though, with one exception, they 
