up by saying that the hydraulic propeller is less efficient
than the screw, because it does more work on the water and less on the
boat; and that the boat in turn does more work on the water than does
one propelled by a screw, because she has to take in thousands of tons
per hour and impart to them a velocity equal to her own. Part of this
work is got back again in a way sufficiently obvious, but not all. If
it were all wasted, the efficiency of the hydraulic propeller would be
so low that nothing would be heard about it, and we certainly should
not have written this article.--_The Engineer._

* * * * *

THE NEW ARMY GUN.

The cut we give is from a photograph taken shortly after the recent
firings. The carriage upon which it is mounted is the one designed by
the Department and manufactured by the West Point Foundry, about six
months since. It was designed as a proof carriage for this gun and
also for the 10 inch steel gun in course of construction. It is
adapted to the larger gun by introducing two steel bushing rings
fitted into the cheeks of carriage to secure the trunnion of the gun.

The gun represented is an 8 inch, all steel, breech-loading rifle,
manufactured by the West Point Foundry, upon designs from the Army
Ordnance Bureau. The tube and jacket were obtained from Whitworth, and
the hoops and the breech mechanism forgings from the Midvale Steel
Company. The total weight of the gun is 13 tons; total length,
including breech mechanism, 271 inches; length of bore in front of gas
check, 30 calibers; powder space in chamber, 3,109 cubic inches;
charge, 100 pounds. The tube extends back to breech recess from
muzzle, in one solid piece. The breech block is carried in the jacket,
the thread cut in the rear portion of the jacket. The jacket extends
forward and is shrunk over the tube about 871/2 inches. The re-enforce
is strengthened by two rows of steel hoops; the trunnion hoops form
one of the outer layers. In front of the jacket a single row of hoops
is shrunk on the tube and extends toward the muzzle, leaving 91 inches
of the muzzle end of the tube unhooped. The second row of hoops is
shrunk on forward of the trunnion hoops for a length of 38 inches to
strengthen the gun, and the hoop portion forms three conical frustums.
The elastic resistance of the gun to tangential rupture over the
powder chamber is computed by Claverino and kindred formulas to be
54,000 lb. per square