THE THUNDERER.

The Thunderer is a sister ship to the Devastation, launched March 12, 1872, nearly one year after the Devastation, but was only being prepared for the first commission at the time of my visit, early last summer. The principal dimensions of the two vessels are alike; they differ only in detail of construction, in the type of motive-machinery, and in arma

ment.

The Thunderer, like her sister ship, was designed to be thoroughly sea-going, and to be capable of performing every service which can be required from a first-class modern line-of-battle ship.

At the date of construction they were admitted to be the most powerful fighting-ships then laid down. The committee on designs of the ships of the royal navy gave their judgment upon them in these words: "They represent in their broad features the first-class fighting-ships of the immediate future."

A clear understanding of the general arrangement of the vessel will best be seen by the drawings annexed, figures 1, 2, and 3. The forecastle is shown at A, in figure 1, where the height of the side-armor above and below water is also shown. The position of the armored deck is indicated by the black line along the upper edge of the side-armor. In Fig. 1 the armored portions are shaded, the unarmored left plain. Where the armor is visible from the outside, as on the turrets and sides, it is shaded dark; where concealed by any unarmored structure it is lighter. The breastwork, except at one corner where it is not screened, is shaded light in Fig. 1, being concealed by a structure to be noticed hereafter.

An end view of the deck-house, and the hurricane-deck which it supports, is seen in Fig. 3, a section through the fore turret. The broadside superstructure, as it is usually called, is shown at B B in Fig. 1, and at EE in section 3. The superstructures and other parts are clearly shown in the plan, Fig. 2, where, commencing with the highest points, I I are the smoke-pipes, H is the conning-tower, A A the hurricane-deck, B the elevated deck-house which supports it, CC are the turrets, D the breastwork, E E the broadside superstructure level with the breast work, F the forecastle, 3 feet lower than the breastwork, and G the armored deck, about 7 feet lower than the breastwork in the only part where it comes in sight, though it extends, of course, under E and F, and, indeed, throughout the ship except inside the breast work. The same letters apply to Fig. 3. The conning-tower will be noticed in Fig. 1. It is sufficiently high to give a view over the hurricane-deck bulwarks, and wide enough to command a view forward and aft past the smoke-pipes, which are oval.

MACHINERY.

The Thunderer, in common with all modern fighting ships, is operated in every essential particular by the power of steam. The motive-power of the ship is solely steam, and there are in all twenty-eight steam-enS. Ex. 27-4

gines and nine boilers. Thirteen of these engines are in pairs, having two cylinders, and the remaining fifteen are single engines, having one cylinder only. Two of the pairs are employed for driving the twin screws, and are termed the motive-engines. The others are small engines, employed for subsidiary purposes, such as revolving the turrets, working the hydraulic gun-machinery, hoisting shot and shell, working the capstans, hoisting anchors and boats, working the steering-apparatus, working pumps for circulating cold water through the surface-condensers, starting the motive-engines, pumping water from the spaces between the double bottoms, feeding the boilers, hoisting ashes, and driving fans for ventilating the ship. In addition to this great responsibility, the engineer department is charged with all the water-tight doors in the ship. and all valves and pipes. In short, the interior of the ship is a vast engineering workshop, requiring skill and energy successfully to manage

it.

The motive-machinery of this vessel, as well as that of the Derastation, was contracted for previous to the introduction of the compound engine into the royal navy. It wasconstructed by Messrs. Humphrys Tenant & Co., and the engines are of the horizontal, direct-acting type adopted by that firm, and built for several other ships of the navy. There is one pair to each of the two screw-propellers; the cylinders are 77 inches in diameter, and the stroke is 3 feet 6 inches. The boilers are of the old box variety, and a description of them follows, under the head of "boiler-explosions." In consequence of the explosion of one of the boilers in July last, the final official trials at the measured mile have just been made; and the following data of the performance are believed to be correct.

Two days after the measured-mile trials on the 4th of January, 1877. a crucial test of the working of the machinery by a six hours' continuous full-power run was made up and down the Solent in boisterous weather, the force of the wind being between seven and nine, and the sea rough; the following results were obtained as the means of the twelve half hours:

Pressure in boilers....

Vacuum, starboard forward engine.

Vacuum, starboard after engine.

Vacuum, port forward engine.

Vacuum, port after engine..

Revolutions per minute, starboard

Revolutions per minute, port......

27.80 pounds.

27.3 inches.

25.79 inches.

27.99 inches.

25.52 inches.

75.20

75.03

19. 491 pounds.

Pressure in cylinders per square inch, starboard

Pressure in cylinders per square inch, port........

19.25 pounds.

Indicated horse-power, 5,748.97, or 149 horse-power beyond the contract.

The best quality of Nixon's steam-navigation coal was used, and the expenditure was 3.14 pounds per indicated horse-power per hour.

ARMAMENT.

The Thunderer was originally fitted, like the Devastation, with two 35-ton, 12 inch Woolwich rifled guns in each of the two turrets, mounted on carriages similar to those of the Glatton, and known as Captain Scott's design; but after Mr. Rendel brought out his system for working heavy guns by hydraulic pressure, it was decided to introduce the prin ciple for the first time into the forward turret of this vessel. Accord ingly the two 35-ton guns were removed, and guns thirty-eight tons in