190 REPORT—1857. 
Without working in a tube—Effects produced by a two-bladed 
screw-propeller, similar to the common screw, in diameter 133 inches 
and 20 inches pitch, area 1 square foot, but having a portion of the 
interior of its blades cut away in hollow curves,—176 lbs. 
Without working in a tube.—Effects produced by a two-bladed screw-pro- 
peller, 134 inches diameter and 20 inches pitch, but tapered at the outer 
extremities of the blades in a parabolical form thus :—137 lbs. Area of circle 
1 square foot. 
The above experiments were varied in many ways both in speed and depth; but 
the mean pressures which are given are sufficiently approximate. The greatest result 
is given by the curved-bladed propeller. 
Apparatus for trying the resistances of different Screws when immersed at similar depths 
in the River Thames. 
a a 
CAST IRON CISTERN 
4 
2 
! 
Level of Water 
Level of Wator 
f 
On the Quantity of Heat developed by Water when rapidly agitated. 
By Georce Rennie, RS. 
My last paper, communicated to the Mechanical Section of the British Association 
at Cheltenham, in August 1856, contained a brief notice of the experiments which © 
had been made upon this subject by Count Rumford, and by Mayer, Joule, Thom- 
son, Rankine, &c. The mechanical equivalents which were estimated by those — 
philosophers therefrom, and the heat developed by chemical as well as by mechanical 
action, were briefly noticed; and the causes which led to the making the experiments 
were shown to have originated in the development of heat observed by me in the sea” 
in stormy weather, and when water ran through sluices at Southampton Dock and 
other confined apertures. As formerly stated, the experiments were made by agitating 
rapidly a mass of 437 lbs. of well-water confined in a cubical box, until its tempera- 
ture became elevated from 59° Fahrenheit’s thermometer to 1032° by the same 
