226 Mr. W. C. Dampier Whetham. On the alleged [June 19, 



Thus the flow through a gilt tube of a millimetre in diameter 

 should be twenty times as fast as through a tube where there is no 

 slip. Poiseuille showed that for a glass tube X = 0, and it had been 

 generally supposed that this also held for other substances wetted by 

 water. 



Such a large effect as the above shows that the existence of the 

 coefficient would be much better investigated by transpiration experi- 

 ments than by oscillating spheres, and an investigation has been 

 carried out on these lines. 



In order to prevent absolute determinations, the time of flow of a 

 known volume of water through a glass tube was observed, the inte- 

 rior of the tube silvered, and another observation taken with the 

 same pressure and the same volume of water. 



FIG. 1. 



I. The water was allowed to run out of a bulb through the transpi- 

 ration tube under its own pressure. 



As the result of four series of observations on three different 

 tubes, it was found that the times of flow for the glass tubes were the 

 same to within O7 per cent, as the times for the silvered tubes, cor- 

 rections being made for changes of temperature, and for the decrease 



