-314 Prof. 0. .Reynolds on certain Dimensional [Feb. 6, 



These results, in as far as the conditions correspond, were found to 

 agree very closely with the results obtained by Graham. Thus, 

 through stucco at 30 inches, the comparative times of transpiration of 

 air and hydrogen were as 2*9 to 1, Graham's results being 2*8 to 1. 

 Through meerschaum the ratio was 3*6 to 1, Graham having found the 

 ratio 3'8 to 1 through a graphite plate, which was in all probability 

 finer than the meerschaum. The ratio of the times of transpiration of 

 equal volumes of different gases, which Graham looked upon as vary- 

 ing only with the coarseness of the plates, was found, as was expected, 

 to depend entirely on the relation between the pressures of the gases 

 and the coarseness of the plates, the ratio of the times being the same 

 as long as the pressures of the gases were inversely proportional to 

 the coarseness of the plates. 



Thus, at a pressure of 5 inches, the times for hydrogen and air 

 through stucco, instead of being 2*9, as at the pressure of the atmos- 

 phere, were 3' 6, or the same as through meerschaum at a pressure six 

 times as great; the coarseness of the plates, as determined in the 

 previous experiments, being 5'6. The same agreement held as long as 

 the ratio between the pressures was maintained. 



The correspondence of the results for different plates, and the com- 

 plete verification of the theoretical conclusions which they afforded, is 

 shown by comparing the logarithmic homologues of the curves in 

 which the times of transpiration are the ordinates and the pressures the 

 abscissae. The fitting of the logarithmic homologues is exact, both as 

 regards the direction of the curves and the distances between the 

 curves, for air and hydrogen ; the displacement along the abscissas, to 

 bring the curves into coincidence, being "819 = log. 6*5. 



As this number, 6'5, is the ratio of the coarseness of the plates, it 

 should have corresponded with the ratio obtained by thermal transpira- 

 tion, which was 5'6, with the same plates. This discrepancy, although 

 too small to cast a doubt upon the general agreement of the results, is 

 too large to be attributed to experimental inaccuracy, and must have 

 been due to some change in the plates, probably arising from the 

 plates being hot in the one case and cold in the other. 



Experiments on Impulsion with a Suspended Fibre. 



A single fibre of unspun silk was suspended from one end in a 

 vertical test-tube, closed with an india-rubber cork, and connected with 

 an air-pump, and a microscope was arranged for observing the motion 

 of the fibre when a hot body was brought into a certain position near 

 the test-tube. 



With air in the test-tube at the pressure of the atmosphere, it was 

 found that the fibre was carried by the air- currents towards the hot 

 body, and this was the case as long as the pressure was greater than 

 8 inches of mercury, but after the tube had been exhausted below 



