PHYSIOLOGY OF THE CIRCULATION. 75 



The junction of tins tube with the short vertical 

 branch was made water-tight, and the descent 

 of the former into the main passage, through the 

 tin pipe, was of course rendered impossible by the 

 minuteness of the communicating apertures. The 

 wooden vessel or reservoir was then filled with water 

 to a height of twelve inches above the entrance of 

 the tin pipe, and the column in it was maintained at 

 the same elevation by the constant addition of fresh 

 fluid. On removing a plug which had been pre- 

 viously placed at the inner orifice of the tin pipe, 

 the water rushed through the latter, and escaped in 

 a jet, sweeping, in this course, across the minute 

 apertures which communicated with the interior of 

 the glass tube. 



During the whole of the time that this flow con- 

 tinued, there was no ascent of water in the glass 

 tube ; showing that, if the stream traversing the tin 

 pipe did exert any lateral pressure, its amount was 

 so inconsiderable as to be incapable of raising a 

 column of water to the height of one inch ; for it 

 would then have been perceptible in the tube. 



Exp. 2. The apparatus being in every other 

 respect untouched, a short straight tube, one-third 

 of an inch in diameter, was so fastened into the centre 

 of the outer orifice of the tin pipe as entirely to 

 prevent any escape of fluid from the latter, with the 

 exception of that which passed through this smaller 

 tube. The height of the column maintained in the 

 reservoir was the same as in the last experiment, viz. 

 twelve inches. On then allowing the water to enter 

 the tin pipe, and escape freely through its narrowed 



