294 Prof. 0. Reynolds and Mr. W. H. Moorby. 



water flowing through the brake, the magnitude of which stream is 

 independent of the load on the brake or the speed of the engine,, 

 and is under independent control. 



The existence of the Manchester town water, of a purity expressed 

 by 3 grains of salts to the gallon, conveniently distributed in the 

 laboratory, as well as auxiliary power, both steam and water. 



Although unconsciously, the research was really commenced in 

 1890, when, without any intention of making a determination of the 

 heat equivalent of the work done on the brake, but solely for the 

 purpose of verifying the mechanical balance of the brake, provision 

 for thermal measurements was added, and a system of trial instituted., 

 in which the object sought was only that of obtaining consistent 

 results over definite portions of the scales of uncorrected ther- 

 mometers, eliminating the errors resulting from radiation by taking- 

 the differences of two trials. In these trials the temperature ranged 

 from 40° to 50° F., and their development was continued over two- 

 years. Then it occurred to Professor Reynolds that by the same 

 method the great facility which this brake was then seen to afford 

 would be available for the independent determination of the- 

 mechanical equivalent, if it could be arranged that water should 

 enter the brake at the temperature of melting ice, and leave it at that- 

 of water boiling under the standard pressure. Since then all that 

 would be required of the thermometers would be the identification of 

 these temperatures, and with a range of 180°, small errors would be- 

 comparatively of small importance. At first the difficulties seemed 

 formidable ; but on trying by gradually diminishing the supply of 

 water to the brake when it was absorbing 60 H.P., and finding that it- 

 ran steadily under control of its automatic gear till the temperature 

 was within three or four degrees of boiling, he further considered 

 the matter, and during the next two years convinced himself of the 

 practicability of the necessary additional appliances by preliminary 

 designs. These consisted in — 



1. An artificial atmosphere or means of maintaining a steady air 

 pressure of 4/3 atmosphere in the air passages of the brake. 



2. A circulating pump and water cooler, by which the entering 

 water, some 30 lbs. a minute, could be forced through the cooler into 

 the brake at a temperature of 32°, having been cooled by ice from 

 the temperature of the town main. 



3. A condenser by which the water leaving the brake at 212 c> 

 might be cooled down to atmospheric temperature before being dis- 

 charged into the atmosphere and weighed. 



4. Such alteration in the manner of supporting the brake on the- 

 shaft as would prevent excess of leakage from the bushes in conse- 

 quence of the greater pressure of air in the brake, since not only 

 would the leaks be increased but when the rise of temperature was 



