370 
POPULAR SCIENCE REVIEW. 
but could not drive it through : the hollow stringers held their 
grip too well. They skidded or ‘^braked” the shot, just as an 
iron strap pressed down by a lever stops the running of the 
wheel of a crane or a machine. Only the hollow stringers 
riveted up along the whole length of their flanges held a good 
deal tighter. Here, then, is a new element of resistance in 
direct proportion to the depth of the stringer, and the depth of 
the stringer directly increases the support of the armour and 
the general strength of the shield. In solid plates one would 
seem to have the full strength of the metal, presuming the 
manufacture to be in all cases equally good ; and we have 
always been led by the Grovernment reports to regard the resis- 
tive capacity of armour-plates as increasing in the proportion of 
the squares of the thickness. Thus, taking a 1-inch plate as 
the unit, we should from nine 1-inch plates obtain a combined 
resistive power of 9 ; but from a solid 9-inch plate we should 
have a resistance of 81, whatever the value of that amount 
might be, and which of course would vary with the quality of 
the iron or material employed. Certain special experiments 
have been made for, and referred to, in connection with the 
plate-up on-plate system, which should cause some slight modi- 
fication of this rule to be acknowledged when combinations of 
very thick plates are employed ; but, nevertheless, it may be 
still adhered to in ordinary and not actually exact considera- 
tions, the difference being a moderate percentage, and not a 
vital or very largely important element. This view would 
incline one towards solid plates properly backed, and induce 
to the encouragement of their more perfect, although more 
costly, manufacture. Seeing the great power of the hollow 
stringer, one is tempted, however, to ask if more strength can 
be got out of the material by a judicious disposition of it in 
layers than exists in the solid plate. Let the following experi- 
ment reply. It was made with a falling weight, for the purpose 
of testing the resistance of the hollow stringer riveted to two 
I -inch plates having a bearing of eighteen inches, as against 
pieces of 4-inch, 5-inch, and 6-inch plates, of the same width 
as the hollow stringer, and similarly supported : the tables 
on page 373 show the results. 
Money is the sinew of war, as of all other terrestrial opera- 
tions ; and the man who economises his little is better off, and 
produces better results, than the thoughtless spendthrift. Even 
rich nations cannot afford 40L a ton for an expensive material 
in an expensive form, if it can get a cheaper material in a more 
useful form for 18^. The rolling of these hollow stringers is a 
cheap operation ; they are light and manageable, and can con- 
sequentl}^ be most rapidly turned out — no re-heatings are 
required, no planings, no risks, no failures, no constant tendency 
