FEICTION BETWEEN WATEE AND AIE. 
591 
of the water vein, I placed a heavy stand (M) with three movable arms on the above- 
mentioned board. Each of these arms ends in a ring with three screws, to hold a tube 
in the middle. The uppermost ring (N) serves only for securing the crosspiece, the 
longest arm of which is held up by it. As to the rest this arm does not differ from 
similar contrivances for chemical purposes. For the other two rings (O, O'), however, 
that have to hold the aspirating tube, one must have two horizontal motions perpendicular 
to each other and worked by screws. This is done in the following manner : — The sliding 
piece P, that belongs to ring O, bears a four-sided horizontal hole, into which fits a four- 
sided brass bar Q, the posterior end of which is worked into a screw. The nut R to this 
screw is held by a fork S fixed to the sliding piece, and the turning of this nut makes 
the bar move forward and backward. On one side of this bar is fixed the end of a strong 
spring T that bears in front the ring O. The spring presses against a screw U that goes 
horizontally through the four-sided bar, and that brings the ring to move nearly in a 
straight line from right to left. 
About the measuring tube I have still to say that it forms a knee with two unequal 
arms. The shorter arm has also an outer radius of IT centim., and is united, as I men- 
tioned before, with one of the horizontal arms of the crosspiece by a short caoutchouc 
tube. The other arm of the knee is generally directed downward, and forms the proper 
measuring tube ; its radius was taken of various sizes, exact measurements requiring a 
larger radius ; it was then necessary to make the measuring tube of two pieces, that 
were united air-tight by cork and sealing-wax. 
The motion of the air caused by the aspiration of the jet of water can now easily be 
rendered visible by means of soap-laminae. If the open end of the measuring tube is 
immersed in a solution of soap, and if we remove this solution slowly, it leaves behind 
a lamina that immediately begins to follow the motion of the air in the aspirating tube. 
The whole measuring tube being wetted inside, such laminae travel even through the 
horizontal part of the tube, till they burst at the mouth of the aspirating tube. One 
can also get a nearly infinite number of laminae to ascend one after the other at the 
same time ; and in this case the laminae keep still better, as the velocity of the whole 
movement decreases with their number. 
If we want to measure * the volume of the aspirated air, we shall employ a single 
lamina, and fix on the measuring tube a paper scale, by which we can determine the 
course of the lamina in one second. This quantity and the inner radius of the tube 
give the aspirated volume most easily. 
There is still another way to study the motion of air caused by a jet of water by means 
of the described apparatus. In this case the measuring tube is replaced by one of metal. 
The open end of it is directed downward, and the flame of a turpentine-lamp is held in 
it. The intense smoke of such a flame reveals immediately vehement motion where all 
seems to be calm. The smoke ascends at the sides of the crosspiece, and descends near 
* This method of measuring volumes of gases was already employed by Dr. T. Eener in his “Eesearches on 
the Diffusion of Gases through Liquid Laminae,” Sitzungsherichte der Wiener Akademie, Band lxx. (1874). 
4 n 2 
