208 
Proceedings of the Royal Society 
Monday , 1st December 1873. 
Sir ROBERT CHRISTISON, Bart., Honorary Vice- 
President, in the Chair. 
The following Communications were read: — 
1. Laboratory Notes. By Professor Tait. 
1. First Approximation to a Thermo-electric Diagram. 
(This Paper will appear in the Transactions of the Society.) 
2. On the Flow of Water through Fine Tubes. 
Dr Matthews Duncan recently ashed me whether the flow of 
blood under given pressure would be affected by a considerable 
change of form of the section of a small vein or artery. It ap- 
peared obvious, from the well-known experiments of Poiseuille 
(which show that when the bore of a capillary tube of circular 
section is sufficiently small, the flow through it. is as the fourth 
power of the diameter), that the flow through a capillary tube 
of elliptical section must be less than that through a circular 
tube of equal sectional area. The accepted theory of fluid friction 
might enable us to obtain, a solution for an elliptic tube, but the 
assumptions requisite for its deduction appear extremely unlikely 
to he fulfilled in practice, so that I asked Messrs C. G-. Knott and 
C. M. Smith to make some direct experimental comparisons between 
various circular and elliptic tubes, specially drawn for the purpose, 
and of the same material. The present preliminary experiments, 
unfortunately, refer only to tubes the smallest of which has nearly 
the bore of the largest of those used by Poiseuille. 
The tubes were carefully calibrated and the worst rejected. A 
length of twenty inches was cut from the most uniform portion 
of each of the selected tubes, and the axes of the section (when 
elliptical) were carefully measured at each end. This determina- 
tion was checked by weighing the column of mercury employed 
for calibration. Water, at a fixed temperature, was drawn under 
