592 
DE. VIKTOE YON LANG ON THE 
the jet of water. There is, of course, an intermediate zone without vertical motion ; but 
in this zone a very violent rotation takes place around a horizontal axis perpendicular 
to the radius. This is shown by larger particles of soot that come by chance into this zone. 
As to the motion of the air in the aspirating tube, the smoke is not dense enough to 
be seen in it when the radius of the tube is very small ; but one sees that the smoke, 
in leaving the tube, continues to surround the jet for some time. This shows that the 
particles of air flow through the tube in parallel lines very regularly. 
The last phenomenon does not take place any more when the radius of the aspirating 
tube becomes larger. In this case one can also see the smoke, and observe by it that 
the motion of the air is now very irregular, although no ascending movement can be 
detected. 
Determination of the Form of the Water-jet. 
The quantity of the aspirated air varies of course with the radius of the jet and with 
the velocity of the water on the surface of it. For finding this latter velocity there 
was nothing to be done hut to suppose the velocity constant for the whole section of 
the jet. The velocity may then be calculated easily from the radius of the jet and 
from the volume of water discharged in one second. These two quantities depend on 
one another for each section of the jet. Having made corresponding measurements of 
them in different places of the jet, we may afterwards compute the radius only from 
the quantity of water discharged. 
The measuring of the radius of the jet was effected by means of a kathetometer placed 
at a distance of 2 metres from the jet. The telescope bears an ocular micrometer, and 
its magnifying power is such that the distance of 1 centim. needs 6 '80 turns of the 
micrometer-screw. I have to add that the quantity of water per second was found by 
weighing the quantity discharged in 5 seconds. 
It would be sufficient for what follows to know the form of the jet from 35 centims. 
below the orifice. But it seems to me that for other problems it might perhaps be 
of interest to know the form of a jet of water beyond that limit also, and therefore I 
shall give my complete observations here. 
In the following Table (p. 593) z denotes the vertical distance from the orifice, W the 
quantity of water discharged in one second, and r the radius of the jet at the place 
given by z. The distance z is measured in centimetres, W in grammes, and r in turns 
of the micrometer-screw. The numbers given for W and r are means from two to ten 
observations. 
The column headed r 1 gives the values of r calculated by the following formulae : — 
2=35 
r= 1-1860+0-045202 W. 
45 
1-1503 + 0-041941 W. 
55 
1-0566 + 0-041354 W. 
65 
1-0606+0-036555 W. 
75 
0-7064+0-049137 W. 
