[Footnote 2:  In consequence of the seas breaking over the boat, a large number of diagrams were destroyed, and, on account of the roughness of the weather, cards were only taken with the greatest difficulty.  The records of power developed are therefore not put forward as authoritative.]

In connection with this subject it may perhaps be of interest to give particulars of a French and American steam launch; these we extract from the United States official report before mentioned.

Steam Launch of the French Steamer Mouche.

Length on low water level 27 ft. 10-1/2 in. 
Breadth 5 ft. 11 in. 
Depth to rabbet of keel 3 ft. 3-1/3 in. 
Draught of water aft 2 ft. 1-1/2 in. 
Weight of hull and fittings 2,646 lb. 
Weight of machinery with water in boiler 3,473 lb.

The boat is built of wood, and coppered.  The engine consists of one non-condensing cylinder, 7-1/2 in. in diameter and 5.9 in. stroke.  The boiler has 4.3 square feet of grate surface.  The screw is 21-2/3 in. in diameter by 43.3 in, pitch.  The speed is 7 knots per hour obtained with 245 revolutions per minute, the slip being 19.7 per cent. of the speed.

The United States navy steam cutters built at the Philadelphia navy yard are of the following dimensions: 

Length 27 ft. 71/2 in. 
Breadth 7 ft. 10 in. 
Depth to rabbet of keel 3 ft. 113/4 in. 
Displacement (to two feet above rabbet of keel) 5.96 tons. 
Weight of hull and fittings 4,675 lb.
   " engine 1,240 "
   " boiler 3,112 "
   " water in boiler and tanks 2,696 "

The engine has a single cylinder 8 in. in diameter and 8 in. stroke of piston.  The screw is four bladed, 4 in. long and 31 in. in diameter by 45 in. pitch.  The following is the performance at draught of water 2 feet above rabbet of keel: 

Boiler pressure 90 lb. 
Revolutions 353
Speed 7.8 knots. 
Indicated horse power. 53

These boats are of 1870 type, but may be taken as typical of a large number of steam cutters in the United States navy.  The naval authorities have, however, been lately engaged in extensive experiments with compound condensing engines in small boats, and the results have proved so conclusively the advantages of the latter system that it will doubtless be largely adopted in future.—­Engineer.

* * * * *

IMPROVED STEAM TRAP.