THE LAW OF RESISTANCE IN PARALLEL CHANNELS. 
951 
difficult to say whether this was due to the wavering of the colour band or to genuine 
eddies. 
21. The final apparatus .—This was on a much larger scale than the first. A 
straight tube, nearly 5 feet long and about an inch in diameter, was selected from a 
large number as being the most nearly uniform, the variation of the diameter being 
less than l-32nd of an inch. 
The ends of this tube were ground off plane, and on the end which appeared 
slightly the larger was fitted a trumpet mouth of varnished wood, great care being 
taken to make the surface of the wood continuous with that of the glass (Plate 73, 
fig. 13). 
The other end of the glass pipe was connected by means of an indiarubber washer 
with an iron pipe nearly 2 inches in diameter. 
The iron pipe passed horizontally through the end of a tank, 6 feet long, 18 inches 
broad and 18 inches deep, and then bent through a quadrant so that it became 
vertical, and reached 7 feet below the glass tube. It then terminated in a large 
cock, having, when open, a clear way of nearly a square inch. 
This cock was controlled by a long lever (see Plate 73) reaching up to the level of the 
tank. The tank was raised upon tressels about 7 feet above the floor, and on each 
side of it, at 4 feet from the ground, was a platform for the observers. The glass 
tube thus extended in an horizontal direction along the middle of the tank, and the 
trumpet mouth was something less than a foot from the end. Through this end, just 
opposite the trumpet, was a straight colour tube three-quarters of an inch in diameter, 
and this tube was connected, by means of an indiarubber tube with a clip upon it, with 
a reservoir of colour, which for good reasons subsequently took the form of a common 
water bottle. 
With a view to determining the velocity of flow, an instrument was fitted for show¬ 
ing the changes of level of the water in the tank to the 100th of an inch (Plate 72, 
fig. 14). Thermometers were hung at various levels in the tank, 
22. The final experiments .—The first experiment with this apparatus was made 
on 22nd February, 1880. 
By means of a hose the tank was filled from the water main, and having been 
allowed to stand for several hours, from 10 a.m. to 2 p.m., it was then found that the 
water had a temperature of 46° F. at the bottom of the tank, and 47° F. at the top. 
The experiment was then commenced in the same manner as in the first trials. The 
colour was allowed to flow very slowly, and the cock slightly opened. The colour band 
established itself much as before, and remained beautifully steady as the velocity was 
increased until, all at once, on a slight further opening of the valve, at a point about 
two feet from the iron pipe, the colour band appeared to expand and mix with the 
water so as to fill the remainder of the pipe with a coloured cloud, of what appeared at 
first sight to be of a uniform tint (fig. 4, p. 942). 
Closer inspection, however, showed the nature of this cloud. By moving the eye 
6 p 2 
