18 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXV.) 
Fig. 4. 
der might be sent through it, and also with a foot or 
stand so that it might be placed in any required posi- 
tion. The end of the tube was drawn down, bent at 
right angles, and cut off straight across at the extre- 
mity, being of the size and shape represented in fig 4. 
2759 . It is easy to blow soap-bubbles at the end of 
such a tube, of any size up to an inch in diameter, and 
retain them for the time required by the action of the 
stopcock. The soapy water should be prepared, when 
wanted (and not beforehand), by putting a cutting or two of soap into a little cold 
distilled water, for then bubbles of the thinnest and most equable texture can be 
blown, which are more mobile than if thicker suds be used, and if a little care be 
taken, quite permanent enough for every useful experiment. The end of the pipe 
should be perfectly clean and free from heterogeneous matter (which is often destruc- 
tive of the bubble), and should be wetted both inside and outside with the soap- 
water, and left awhile in it before 2 ise. 
2760. If a bubble be blown with the end of the tube downwards, and be half an 
inch in diameter, it will usually have a little extra water at the bottom, and will hang* 
from the slender extremity of the tube by an attachment so small as to allow it great 
freedom of motion. Hence it will swing to and fro like a pendulum ; and according as 
there is more or less water at the bottom, it will vibrate more or less rapidly, will, as 
a whole, gravitate more or less powerfully, and therefore will retain its perpendicularly 
dependent position with more or less stability, — circumstances which are very useful 
in the employment of the bubble as a magnetic or diamagnetic indicator. 
2761. The determination of tlje relative quantity of water which is in or upon the 
bubble is easily obtained within certain limits. If, after the pipe is dipped in the soap- 
water, the end be touched with a piece of wood or glass rod, which has also been kept 
in the soap-water, more or less of the liquid may be removed ; and by observing the 
height at which the fluid stands by capillary action within the tube, which may be 
varied between -^oth and ^ an inch, it is easy, after a few experimental trials, to ob- 
serve how much is required to make a bubble charged with a certain amount of 
water, and how little to give a bubble without any dependent water below ; and then 
it is just as easy, by arranging the amount of water beforehand, to blow a bubble of 
any required character. Even when no drop of water is left at the bottom, still a 
range of thickness or thinness in the film itself can be obtained. 
2762. As the bubbles contain less and less of water, so are they rendered more 
sensitive in their action. They vibrate slower, and are more easily moved by forces 
applied laterally to them. The diamagnetic effect of the soap-water constituting 
them is less, and therefore that of the gas contained within them comparatively 
greater. If the bubble is very thin, the dependent position becomes a position of 
unstable equilibrium, for any inclination of the tube, or any lateral force, however 
small, then causes the bubble to pass to one side, and to run up and adhere to the 
