412 Progress in Science. (July, 
to a large extent realised, without the necessity of lifting or lowering the gun 
itself. 
Ships.—At the recent meetings at the Institution of Naval Architects, several 
very important papers were read relating to the form, size, and construction of 
ships. An examination of these in detail would occupy more space than we 
can now give to the subject, and we shall therefore do little more than name 
the several principal features of these papers. The prominent position which 
the question of the proper loading of mercantile vessels has lately assumed, 
has induced Mr. Benjamin Martell, Chief Surveyor of Lloyd’s Registry of 
British and Foreign Shinping, to investigate the question as to what constitutes 
a fair freeboard for sea-going vessels, and he has accordingly prepared a scheme 
of freeboard for the various types of vessels in existence. A set of tables has 
now been published which determine, not a hard and fast load-line, which 
would be impracticable, but a fair line of reference for ordinary trades for the 
various types of sea-going sailing vessels and steamers of the first class. The 
principle governing this load-line is that of allowing acertain proportion of the 
total volume of the vessel above the water, in relation to her size and extreme 
length, and the mode adopted for cutting off this percentage of spare buoyancy 
is by multiplying the registered tonnage under deck by roo, and dividing this 
by the produé of the length, breadth, and depth of the vessel. The quotient 
obtained affords a fair approximation to their relative fineness, from which the 
proper freeboard may be readily traced on the tables. 
Mr. W. John’s paper on the “ Strength of Iron Ships” produces some faéts 
which are sufficient to cause serious alarm, and ought, as he suggested, to 
secure a very careful consideration of the subject. He remarked, with regard 
to the constant tendency to increase the size of vessels, that, although it may 
not astonish anyone to hear that vessels over 300 feet in length are not as a 
rule strong enough to bear being pivoted on a rock or causeway amidships, it 
will probably surprise some to learn that they are liable to a strain of 8 tons 
per square inch afloat. ‘‘ This,” he states, “‘ with the present state of the iron 
manufacture, gives a factor of safety of not more than 23, which would scarcely 
be considered satisfactory by engineers for a land structure.” 
This paper was followed by one by Mr. W. Froude, F.R.S., Vice-President, 
on the “ Useful Displacement as Limited by Weight of Structure and of Pro- 
pulsive Power,” in which it was remarked that the existing tendency towards 
extreme length, as compared with midship section, was only justified where 
extreme speed was required,—speed very much greater than that which sea- 
going merchant ships in fact realise. He drew a conclusion from prior argu- 
ments that the total sectional areas of the deck, the bottom, and the sides of a 
ship must be proportioned to the stress; and, as the structural weight may be 
taken as proportioned to their sectional areas multiplied by the ship’s length, 
it must be regarded as proportional directly to the fourth power of the length, 
dire@ly to the breadth, and inversely to the depth. From this follows the 
remarkable result that, alike whether we enlarge a ship by increasing her three 
dimensions throughout in the same given ratio, so as to enlarge her total dis- 
placement in the cube of that ratio, or whether we enlarge her by increasing 
her length alone, the increased structural weight will be as the fourth power 
of the enlargement of dimensions. It is obvious that in whatever degree the 
total dead weight of a ship’s hull depends on her requirement of structural 
strength, this conclusion tells most unfavourably on the useful displacement 
of a ship enlarged simply by elongation, as compared with one enlarged in all 
her dimensions alike. 
Mr. Nathaniel Barnaby, Vice-President, in a paper ‘‘On some Recent 
Designs for Ships of War for the British Navy, Armoured and Unarmoured,” 
entered into particulars of size, form, and construcive details which could not 
well be given in a condensed form. 
Some very interesting experiments for the determination of the resistance 
of a full-sized ship, at various speeds, by trials with H.M.S. Greyhound, were 
recently instituted by the Admiralty. The conclusion of these experiments 
was, that a comparison between the indicated horse-power of the Greyhound, 
when on her steam trials, and resistance of the ship, as determined by the 
