bottom, a a, and covering plates, e c, chain-riveted. this plan the cells would be open from one bulkhead the other, and with proper water-tight manholes been each bulkhead might, if necessary, be used for rage or for the insertion of tanks in which fresh water ht be kept ready for use.

On the above construction the sheathing plates would ap-jointed, using the keelson angle irons and the interiate T-irons as stiffeners for the cells, as shown in fig.

60, which represents one half of the cellular system at the bottom of a vessel from the keel to the turn of the bilge.

Enlarged covering plates, chain-riveted, for the transverse joints, are of great importance both in regard to the lateral and longitudinal strength of the ship. The resistance to tension would be one-sixth greater than with the ordinary construction, and thus the security of the ship would be greatly increased.

As regards the upper and intermediate decks, there would be no change except the introduction of two cells,

Fig. 60.

one on each side of the hatchways, and four other cells, two on each side of the ship, as shown in fig. 56. In the sectional area of the upper deck it will be observed that in the previous calculation we allowed about 4th as the value of the deck planking in resisting a compressive or tensile strain, and that we made a further allowance of material to the bottom to compensate for the wear and tear of those parts. Hence, the sectional area of iron in the upper deck will be to that in the bottom in the ra of 4 to 6. These proportions have been assumed, bu are in accordance with experimental researches, or so far as we have results bearing on this question;

only requires an extension of such experimental investigations to prove how far these proportions approximate to the correct ratio for resisting the strains at those parts respectively.

A series of well-conducted experiments of this kind are much wanted, and a government grant of 1000l., with a similar grant from Lloyds and from the shipowners' fund, would set the question at rest, and establish in shipbuilding, as in other constructions, true principles, the correct expression of physical laws. It is with the object of

aiding in the attainment of this that I have ventured to make these suggestions. The subject is one of deep importance to the community, one on which we are very deficient in knowledge, and one which will reward investigation, and that with great benefit to the public and to mechanical science, and without injury to existing interests.

Impressed with the conviction that we are still labouring under difficulties from a want of knowledge of the true principles of naval construction, we are encouraged from other movements in looking forward to the time when these difficulties will be removed, and when greater economy in the distribution of the material will be accomplished, from the reduction of the whole system of shipbuilding to the exact laws of science.

In the discussion of this question I have not ventured to inquire into the applicability of the cellular construction to ships of war, and my reason for the omission has been that the effect of shot upon iron ships has yet to be decided upon. I am aware that the Admiralty some years since came to a conclusion adverse to the use of iron, which I am not now prepared to call in question. But the improved condition of our iron constructions, and the increased tenacity of the material, taken in connection with our improved system of gunnery, may afford reasons for

altering that decision, and lead to results favourable to the use of iron as a material for building vessels of war.

With the Whitworth rifled gun, for example, with an oblong flat-ended missile, iron is penetrated by a process that drills or cuts out the core without splintering or tearing up the surrounding surface, and looking forward to still further improvements, the iron ship may be increased with safety under the influence of a more destructive arm than has heretofore been used. Be this as it may, the same principles of construction will apply to the navy as to the vessels of the merchant service; and till it it has been more conclusively proved that iron is inapplicable to the construction of ships for the purposes of war, we may reasonably conclude that this material may ultimately become the best safeguard of Her Majesty's dominions at home and abroad.

[Since the above was written I have deemed it necessary to insert in the Appendix two letters addressed to the editor of the "Times," bearing directly on the defective construction of iron ships. These letters were written after the loss of the Royal Charter by a near and dear relative, and are so much to the purpose, that I should consider myself wanting in duty if I omitted statements of such importance to the public. I have also given a quotation from a recent lecture of Mr. Grantham's, in which he shows with great clearness some of the causes of weakness in our present construction, having arrived, independently, at nearly the same conclusions as myself on the necessity for a large increase of transverse strength.7

282

LECTURE VII.

ON WROUGHT IRON TUBULAR CRANES.

THESE structures are identical in principle with the tubular bridges over the Conway and Menai Straits, and present additional examples of the advantages which may yet be derived from a judicious combination of wrought iron plates in constructions requiring security, rigidity, and great strength.

About ten years ago the first design for a wrought iron crane was submitted to the Admiralty for their approval. It was a crane calculated to afford greater security and facility in the embarkation and disembarkation of heavy stores, and was in other respects better qualified for raising heavy weights than the cranes previously in use. The design was placed in the hands of the Surveyor of the Navy and Mr. Lloyd the Inspector of Machinery, who were so well satisfied as to the superiority of the construction that an order was given to erect six of them, in different positions along the line of quays of the new docks at Keyham and Devonport.

These cranes were all of the same size and strength, and were intended to lift weights of 12 tons to a height of 30 feet above the ground, and to sweep them round over a circle of 65 feet in diameter; so that the projection of the jib was 32 feet 6 inches from the centre of the stem, and the extreme height 30 feet above the working platform.