1/0 



REPORT-^1856. 



The length of the boiler was 8 feet 



The breadth of do. was 4 feet 



The height of do. was 4 feet 



The depth of the water in the boiler was at first regulated so as to have its surface 

 level with the surface of the screw. This depth was subsequently increased to 

 One foot above the level of the screw 

 Two feet do. 



Three feet do. 



The speed of the engine (which was 50 revolutions per minute) was multiplied by 

 different-sized pulleys and bands, so as to cause the screw to make 920 revolutions 

 per minute, and was reduced afterwards to 4G0 (one half) the revolutions per mi- 

 nute. The following were the results : — 



Revolutions Revolutions 



920 per min. 460 per min. 



Pressure. Pressure. 



lbs 



lbs. 



First experiment, water level with top of screw 67 G3 



Second do. water above top of screw 1ft. 299 88 



Third „ „ „ ,, 2 „ 350 112 



Fourth „ „ „ „ 3 „ 448 126 



So that on reducing the results, they approximated to a parabolic curve with high 

 velocities, and a sharper curve with lower velocities. The conclusions derived from 

 these experiments at the meeting at Glasgow in 1855, were, that the water being 

 confined in a boiler by its reaction damaged the results, and were not to be de- 

 pended upon. 



In order, however, to remove further doubts on the subject, I had an apparatus 

 constructed somewhat similar, figure 3, as represented in the accompanying wood- 

 cut, with these differences, that the diameter of the screw was 1 ft. 9 in., and its 

 disc area 346^ square inches, or nearly 2^ times larger than Mr. Apsey's screw. 

 The screw worked on the outside of the cistern, and the lever and weights and 

 pulley were inside the cistern, the water having been kept out by means of a stuff- 

 ing-box let into one of the sides of the cistern, through which the spindle of the 

 screw worked. The experiments were made in the river Thames ; so that as the 

 tide rose or fell, the screw could be driven at different depths outside the cast-iron 

 cistern, while the observations were taken within the cistern. 



The greatest speed at which the screw could be driven, was at the rate of 558 re- 

 volutions per minute, and the following were the results : — 



Experiments made in June, 1856, in the river Tliames, for the purpose of determining 

 the resistances experienced by an ordinary two-bladed screw propeller when driven at 

 a high rate of speed and at different depths. 



The ordinates of the above thrusts are represented by a parabola. 



