228 Royal Society : — Mr. F. Galton on verifying 



is entirely open ; a vertical slit, 1 ft. 10 in. long and 4| in. wide, 

 is cut in the side of tlie cylinder and the slit is glazed with a 

 stout sheet of plate-glass, the joints being made water- and steam- 

 tight by means of india-rubber packing. 



The cylinder is placed inside a wooden box, taller than itself, and 

 1 ft. 5 in. square at its base, the space between it and the sides 

 of the box being filled with sawdust, whilst the exterior of the 

 box is completely covered with kamptulicon, in order to retain 

 the heat of the water in the enclosed vessel as much as possible. 

 An aperture somewhat larger than that in the cylinder is cut in 

 the side of the box in front of it, and is also glazed with plate-glass. 



A lid, containing 3 inches of sawdust, covered with a sheet of 

 kamptulicon, can be shut tightly down on the top of the cylinder 

 and box, the escape of the vapour given off during heating being 

 provided for by means of a steam-pipe. 



Pipes lead from the top and bottom of the water-vessel to an 

 exterior pipe ending in a funnel above and a cock below, so that 

 water may be poured in or drawn off from the vessel as desired. 



The whole is firmly fixed to a stout wooden stand about 2 ft. high. 



(2) The Agitator (see fig. 2). 



A stout and hollow brass axis, 2| in.' in diameter, passes vertic- 

 ally up through the centre of the base of the water- vessel, carrying 

 three sets of helical vanes, one above the other, arranged so that 

 the upper and lower vanes form segments of right-handed screws, 

 whilst the intermediate vanes are left-handed. The inclination of 

 every vane is adjustable. 



The lower end of the axis passes through a stuffing-box in the 

 bottom of the cylinder, and is connected by gearing to a crank- 

 handle projecting outside the apparatus. It can be turned easily 

 by the hand of the observer, who thereby is able to agitate the 

 water throughout the whole depth of the vessel. 



(3) The Heating-Apparatus (see fig. 1). 



This is a copper tube 0*6 in. in diameter, which, issuing from 

 the back of the water-vessel near the bottom, is carried through 

 the wooden casing of the instrument, and is then coiled into a 

 vertical spiral of six turns, gradually diminishing in diameter. 

 The end of the tube is afterwards brought back into the water- 

 vessel. 



A cluster of Bunsen burners being placed beneath the coil serves 

 to heat it and to make the water circulate inside the cylinder, thus 

 warming the whole of its contents. 



Experiment shows that, with the small coil used, 10 gallons of 

 cold water can be boiled in about six hours from the time of light- 

 ing the gas ; in practice, however, when it is required to test ther- 

 mometers near the boiling-point only (mountain thermometers, for 

 example) the apparatus is filled with boiling water out of kettles 

 put on an ordinary fire. 



A cone of sheet-copper is usually placed round the coil as a 

 jacket, in order to retain the heat from the gas-burners as much as 



