474 Royal Society : — 



" Report made to the President and Council of the Royal Society, 

 of Experiments on the Friction of Discs revolving in Water." By 

 James Thomson, Esq., C.E., Belfast. 



[A Committee of the British Association for the Advancement of 

 Science, consisting of James Thomson, Esq., C.E., and William 

 Fairbairn, Esq., C.E., F.R.S., having been appointed "to make 

 Experiments on the Friction of Discs revolving in water, with espe- 

 cial reference to supplying data wanted in calculations relative to 

 the action and efficiency of Turbine Water-Wheels in general, and 

 of Centrifugal Pumps ; and also to make an experimental inves- 

 tigation relative to the action and efficiency of Centrifugal Pumps 

 in general, and the amount of improvement derivable in them by the 

 employment of an exterior whirlpool ; " a sum of £50 from the 

 Government Grant of 1853 was allotted by the Council of the Royal 

 Society in aid of the inquiry. The experiments, as originally con- 

 templated, have been arranged and conducted by Mr. Thomson, 

 and the present Report of his progress is here inserted by order of 

 the President and Council for the information of the Fellows.] 



In last year's Report of the Committee it was stated, that an appa- 

 ratus for making experiments on the friction of discs revolving in 

 water had been constructed, and that experiments had been com- 

 menced with it. I have now further to state respecting the experi- 

 ments for which that apparatus was adapted, that I have since got 

 them completed and carefully arranged for the purpose of obtaining 

 from them laws applicable for practical use. 



I now beg to lay before the Royal Society, as a brief statement of 

 the most essential results, the following general equation to show 

 the relation 1 etween the velocity of revolution of the disc, the dia- 

 meter of the disc, and the mechanical work consumed in friction : — 

 _ y'd' 

 ^~ 90,000' 

 in which rf= diameter of the disc in feet, 



y=number of revolutions of the disc per minute, 

 and z= number of foot-pounds of mechanical work consumed 

 per minute. 



This equation is based on experiments which range for the most 

 part between the limits yd=ld2 and i/d=5l8, and may be used 

 with confidence, as sufficiently correct for most practical purposes, 

 if the product of the number of revolutions per minute and the 

 diameter of the disc in feet be between those limits. It is to be 

 observed that the friction is slightly affected by the width of the 

 water space within the case, and the coefficient 90,000 stated in the 

 formula above is, for simplicity in the present brief report, taken 

 between the coefficients obtained by two sets of experiments with 

 different widths. A full report on the experiments already made, 

 explaining the manner of conducting them and stating the detailed 

 results, would be rather lengthened, and would require drawings 

 and diagrams, for all of which I have carefully preserved the requi- 

 site data ; but before proceeding to put these in form suitable to be 

 submitted to the Royal Society, I am desirous of prosecuting the 



