358 Mr. J. D. Chorlton. Examination of some of the [Mar. 19, 



papers, but Mr. Joule told me that he had never come across any in 

 the house, and did not think that any had been brought to Sale. 



The only book I could find containing notes by Joule was a small 

 book partly filled with memoranda relative to the brewery, at one 

 end is a draft of the paper " On the Determination of the Equivalent 

 of Heat from the Thermal Effect of Electric Currents," at the other 

 end are numerous readings of the barometer, taken day by day, and 

 extending over a period of several months. 



The following extracts are taken from the catalogue of the Collec- 

 tion of Scientific Apparatus at South Kensington. 



Apparatus used by Dr. Joule, F.R.S, for ascertaining the 

 Mechanical Equivalent of Heat. 



218. Revolving Electro-magnet, used in 1843 for ascertaining the 



Mechanical Equivalent of Seat. 



Part of the apparatus used in 1843 for the determination of the 

 mechanical equivalent of heat : viz., a revolving piece, holding a 

 glass tube filled with water, and containing an electro-magnet. This 

 worked between the poles of a powerful magnet; and the heat 

 evolved by the rotating electro-magnet was measured by the rise of 

 temperature of the water. In this manner the quantity of heat lost 

 by the circuit was ascertained when the machine worked as an 

 engine ; and, on the other hand, the quantity of heat produced when 

 work was done on the machine was also measured. 833 ft. -lbs. was 

 the mechanical equivalent of a degree F. in 1 lb. of water, as 

 determined by these first experiments. 



219. Calorimeter, containing a revolving agitator. This was em- 



ployed in the experiments on the heat evolved by the friction 

 of water, made in 1849. The equivalent arrived at was 

 772 ft.-lbs. 



220. Cast-iron Vessel, containing Friction Disk, to revolve under 



mercury. Used in 1849 to determine the mechanical equiva- 

 lent of heat by the friction of cast iron against cast iron. The 

 equivalent arrived at was 775 ft.-lbs. 



221. Electro-magnet consisting of a broad plate of ^-inch iron having 



a bundle of copper wires coiled round it. Employed in the 

 first determination of the mechanical equivalent of heat. 



222. Apparatus for determining the temperature of water at its maxi- 



mum density. 



Used in the experiments on atomic volume and specific gravity by 

 Playfairand Joule (' Memoirs of the Chemical Society,' vol. 3,1846). 

 It consists of two call vessels, connected together by a stop-cock at 

 the bottom, and a trough at the top. A minute difference of the 



