Manchester Memoirs y Vol. xlii. (1898), No. 6. 23 



naked brake would be reduced to one-fourth part with 

 the covered brake, provided no fresh errors, owing to the 

 time taken to get the lagging at a steady temperature or 

 owing to its absorption of moisture, intervened. Further, 

 it was arranged that a similar plan should be adopted to 

 obtain assurance of the elimination of errors resulting- 

 from each detailed circumstance that could effect the loss 

 of heat, namely, that, where such circumstance could not 

 be removed, its effect should be definitely varied and a 

 fresh set of trials run, which plan seemed to afford the 

 best possible means of determining the limits of error. 



The leakage of water from the three working joints 

 of the brake was a matter of first consideration and 

 continual care. By continual attention to the stuffing- 

 box and gland it was reduced to a very small amount. In 

 so far as the leakage was equal in the light and heavy 

 trials, the effect of such leakage would be eliminated ; 

 and, to ensure this, the water was caught, its temperature 

 on leaving the brake measured, and the losses of heat 

 allowed for, so that the possible limits of error from this 

 cause, which were very small, were somewhat definitely 

 ascertained. 



The losses of water by evaporation from the surface 

 in the tank, &c., were rendered as nearly as possible equal 

 for the light and heavy trials by cooling all the water tc 

 a fixed temperature before exposure to the atmosphere, 

 it being arranged that, after the experiments were over, 

 the appliances should be so altered as to admit of the 

 water in the weighing tank at the working temperatures 

 being forced round the same circuit from the weighing 

 tank back to the weighing tank, for one hour, at the rates 

 of entrance in the light and heavy trials respectively, so 

 that the actual losses in each of these trials should be 

 ascertained. 



By these means, definite estimates of the outside limits 



