538 
POPULAR SCIENCE REVIEW. 
taining the longitudinal metacentre of a vessel, a problem which enables 
us to determine the effect of shifting the weights fore and aft on a vessel’s 
trim. Mr. G. B. Airey, the Astronomer Royal, described a mode of 
steering or slewing a vessel by means of a screw-propeller, placed in the 
dead wood near the stern-post with its axis athwartships. Several papers 
w T ere read on rudders and steering, amongst which may be mentioned that 
of Mr. Barnes, proving that for a given amount of power at the helm a 
small rudder, brought over to the full rudder angle, is more efficient than 
a larger rudder at a less angle. Also an account of some trials favourable 
to the use of a partially-balanced rudder, by Commander Shuldham, R.N. 
Admiral Sartorius advanced the claims of the steam-ram, whilst Sir E. 
Belcher, who sets a low value on the ram, from the difficulty of striking 
a ship in motion, proposed that war-vessels should be defended by an 
outer iron casing resting on longitudinal stringers, with an interior iron- 
cased cell of oval section containing the boilers and engines, the space 
between the outer and inner casing forming air-tight cells to be used as 
coal-bunkers. Mr. Norman Scott Russell discussed the relative advantages 
of turret and broadside arrangements of guns, arriving at the conclusion 
that the turret should only be used in moderate sized vessels, carrying 
one or at most two cupolas ; in other cases, the broadside arrangement 
had a decided superiority. Mr. McLaine advocated a system in which 
the guns fire only in the line of the keel, the vessel having twin screws, 
so that the lateral training of the guns is effected solely by steering, 
the ship always fighting bow on. Capt. Symonds introduced the subject of 
twin-screw vessels. Mr. E. A. Cowper read a paper on uniform power 
expansive marine engines, in which the use of the steam jacket is 
extended, and a reservoir provided to receive the steam from the high- 
pressure cylinder until, the cranks having passed round 90, the low- 
pressure cylinder is ready to receive it. Among several remarkable 
papers by Dr. Rankine, the most practically interesting was one on the 
computation of the resistance of proposed ships, from which the speed 
with a given engine power and the engine power necessary for a given 
speed may be ascertained. 
Experiments on Armour Plates . — Further experiments at Shoeburyness 
confirm the high opinion already formed of the Chalmers system of 
armour-plating. The target consisted of a facing of 3f-inch plates, backed 
by 10 inches of teak and an inner casing of 1^-inch plates connected with 
the facing by f-inch iron webs between each balk of interposed timber. 
The inner plating rests on five inches of teak, and this again on the skin 
of the vessel f-inch thick. It proved entirely invulnerable to all service 
projectiles, but w T as pierced by the 300-pounder. 
Palliser's Bolts . — Captain Palliser has introduced a singularly scientific 
improvement of the bolts for armour-plates, which overcomes the grave diffi- 
culties in their attachment to the ship hitherto existing. He causes the bolt 
to be turned down throughout its length to the diameter of the metal at the 
bottom of the screw-threads. Hence the strain on the impact of a shot, 
being equally intense throughout its entire length, the bolt elongates, acting 
as a perfect cushion or spring, instead of chipping off immediately below 
the nut. 
