5o6 



NA TURE 



\April 2i,\%12 



for ascertaining the mechanical energy developed by the 

 radiation of the fused mass under consideration. Fig. i 

 represents a vertical section, and Fig. 2 a perspective view. 

 a is a cylindrical boiler, having a flat bottom, composed 

 of thin sheet-iron 0012 inch thick, coated with lamp- 

 black. The cylindrical part of this boiler is surrounded 

 by a concentric casing b, the intervening space being filled 

 with a fire-proof non-conducting substance. A horizontal 

 wheel, c c, ])rovided with six radial paddles, is applied 

 within the boiler, attached to a vertical axle, d. An open 

 cylindrical trunk, g, is secured to the perforated disc which 

 supports the paddles. The vertical axle passes through 

 the top of the boiler, a conical pinion being secured to its 

 upper termination. By means of a vertical cog-wheel, //, 

 attached to the horizontal axle /■, and geared into the coni- 

 cal pinion, rotary motion is communicated to the paddles. 

 The centrifugal action of the latter will obviously cause a 

 rapid and uniform circulation of the water contained in 

 the boiler— indispensable to prevent the intense radiant 



heat from burning the bottom. The boiler and mechanism 

 thus described are secured to a raft, / /, composed of fire- 

 bricks floating on the top of the fluid metal. By this m^ais 

 it has been found practicable to keep the bottom of the 

 boiler at a given distance, very near the surface of the 

 fused mass, while by moving the raft from point to poini, 

 during the observation, irregular heating resulting from 

 the reduction of temperature of the surface of the metal, 

 under the bottom of the calorimeter, has been prevented. 

 The radiant heat being too intense to admit of the axle I 

 being turned directly by hand, an intervening shaft, eight 

 feet long, provided with a crank handle at the outer end, 

 has been employed for keeping up the rotation of the 

 paddle-wheel during the trial. It is scarcely necessary to 

 observe that, the intervening shaft should be coupled to 

 the gear work by means of a "universal joint," to admit 

 of the necessary movement of the raft. The experiment, 

 repeated several times, has been conducted in accordance 

 with the following explanation. The boiler being charged, 



the paddle wheel should be turned at a moderate speed 

 while observing the temperature of the water, the ther- 

 mometer employed for this purpose being introduced 

 through an opening, ni, at the top of the boiler. The tem- 

 perature being ascertained, the instrument should be 

 quickly placed on the raft, and the time noted. As soon 

 as vapour is observed to escape through the opening at 

 m, the instrument must be instantly removed, the time 

 again noted, and the temperature of the water within the 

 boiler ascertained. It will be well to keep the paddle- 

 wheel in motion until the last observation has been con- 

 cluded. 



The temperature of the fused metal having been as 

 high during our experiments as that of the solar surface 

 computed by Pouillet and his followers, while the thin 

 substance composing the bottom of the calorimeter has 

 been biought almost jn contact with, and consequently , 

 received the entire energy transmitted bv, the radiant 

 surface, the reader will be anxious to learn what amount 

 of dynaniic energy has been communicated in a eiven ' 



time, on a given area. The desired information is con- 

 tained in the following brief statement : — The necessary 

 corrections baing made for heat absorbed by the mate- 

 rials composing the paddle-wheel, &c., the instituted test 

 shows that the temperature of a quantity of water weigh- 

 ing 10 pounds avoirdupois has been elevated 121° F. in 

 164 seconds (273 minutes), the area exposed to the radiant 

 heat being 63 square inches. Hence a dynamic energy 

 10 X 121 ^ 144 .1. , • . , 



X -^ = 1013 thermal units per minute, has 



273 63 



been developed by the radiation from one square foot of 

 the surface of the fused metal maintained at 3,000° F., 

 against 312,500 units developed by the radiation of one 

 square foot of the solar surface, the temperature of which, 

 agreeably to the calculations of the French sdvans, is 

 less than that of our experimental radiator. 



Having thus ascertained practically the amount of 

 dyharnii; >;n,i_g^' developed by the radiation of a metallic 

 body raised't'q thli 'bigli temperature of 3,000°, we have 

 only to shov/ iri a similar nianilfer' the amount of energy 



