SCIENCE. 
301 
regard to this powerful viscidity, relates several experi- 1 
merits which make the fact of its existence very percepti- j 
ble. Let us quote the following which is merely the con- 1 
tinuation of one I have already drawn attention to : 
A bubble is blown from a moderately wide tube which, 
however, has a broad mouth, and the other end is then 
left perfectly free. The bubble decreases gradually in 
size, but not in a perfectly systematic manner. On the 
contrary it elongates and at the same time contracts trans- 
versely, assuming a series of longitudinal folds or wrinkles. 
M. Marangoni explains this fact by stating that owing to j 
the diminution of the surface, the coating of dirt becomes 
supersaturated and consequently the tension is annulled or 
reduced almost to nothing, inasmuch as the thin layer 
forming the bubble thus wrinkled and of a nearly conical 
shape does not show any tendency towards the minimum 
of the surface. But, he adds, if the unoccupied end of 
the tube should be corked so that the bubble would not 
decrease in size, the form of the latter would grow gradu- 
ally round, and at the same time it would expel from the 
bottom certain drops of frosty moisture which forms in 
the little folds or wrinkles we have already mentioned ; 
then the coating of dirt would resume its normal condi- 
tion, and the bubble assume, once more, a spherical shape. 
M. Marangoni supposes that apart from the wrinkles 
on the bubble, the tension is utterly null or very nearly so: 
No w, the existence of any liquid utterly devoid of tension 
would be very extraordinary and we may say hardly prob- 
able. Moreover, the drops of moisture in the interior of 
the bubble, being the liquid which constitutes the outer 
coating of dire, should possess little or no tension. I have 
collected these drops upon the crystal of my watch, and 
alter repeating the experiment a number of times, I finally 
procured enough of the liquid to attempt the formation 
of bubbles by means of it. (I must state here that these 
drops were purely liquid and not at all frothy like those 
M. Marangoni describes.) Now, bubbles were formed 
from this liquid, some of them extending three inches in 
diameter, that is to say, they were similar in proportion 
to those obtained by means of the saponaceous solution ; 
only, with the liquid collected from the drops in the crys- 
tal, this maximum was much more difficult to reach. 
In a word, I modified M. Marangoni’s experiment in a 
manner calculated to render his explanation of it still 
more improbable. A bubble about two inches in diam- 
eter was blown from the pipe and the drop suspended 
from the bottom removed ; then, inasmuch as the tube 
was expressly narrow, the wrinkled and cone shaped 
form was produced by inhaling through it, and before the 
drop produced at the extreme point of the cone could 
fall, the pipe was turned upside down in such a way that 
the liquid forming the drop ran along the surface of the 
bubble and separated' itself as much as possible on the 
exterior. Now, although the superficial coating thus 
conserves very nearly its former consistency, and as con- 
sequently (according to M. Marangoni), the tension be- 
comes, so to speak, annulled, the bubble instantly re- 
sumed its spherical shape while the pipe was being turned 
upside down, the time thus occupied not being more 
than one second. This experiment was repeated several 
times and always with the same result. 
In my opinion these facts can be explained very simply. 
When you breathe through the pipe, should it be moder- 
ately wide or even narrow, the bubble necessarily contracts. 
It consequently becomes of a thicker consistency and a 
surplus amount of liquid flows towards the lower extrem- 
ity: but the strong viscidity of the superficial coatings 
renders the general augmentation of density, and the 
equal contraction on all sides, very difficult during the 
short interval of reduction. The surface wrinkles in very 
much such a manner as a small bladder would should 
the air within it be inhaled, and at the same time it elon- 
gates into a conical form from the weight of the liquid 
which accumulates at the bottom. Nevertheless, this 
liquid arising from the increased density of the bubble 
does not notably diminish the tension, as is shown by the 
fact that when the pipe is held upside down and the 
liquid rests upon the bubble sitelf, the latter regains its 
spherical form immediately. 
In regard to the superficial coating of the solution of 
soap, M. Marangoni observed that if this coating was 
viscous it should wrinkle when before the needle, which, 
however, does not occur at all. In order to discover 
what really takes place in reference to this circumstance, 
I began the experiment once more by sprinkling the sur- 
face of the solution with pollen 1 just before liberating 
the needle. If attention is then drawn to the tension of 
the needle, it will be seen that on the side toward which 
this half advances, and until a moderate distance is 
reached, the dispersion of the pollen is diminished, while 
on the opposite side — that is to say, behind this particu- 
lar half — it is considerably increased. Thus, the super- 
ficial coating in front of the needle, instead of puckering, 
contracts, and dilates behind it. Now, if we reason in 
accordance with my theory, and consequently do not ad- 
mit the existence of a coating of dirt, we should acknowl- 
edge that in the portion constructed the molecules per- 
taining to the superficial coating have left it and entered 
the interior of the mass, and also that in the dilated por- 
tion the molecules belonging to the interior have annexed 
themselves to the superficial coating in order to maintain 
the density ; these two effects could not be produced, 
moreover, unless a certain amount of resistance existed. 
They have necessarily developed also a difference of ten- 
sion ; but, in the second of the two series of estimates 
which I effected in reference to the duration of the 
needle’s movements on the surface and in the interior of 
the solution, the temperature was about 21 0 , and from 
M. Marangoni’s observations upon the spherical cavities 
before mentioned, it follows that at this degree of temper- 
ature the differences of tension should possess but slight 
influence. However, the ratio concerning the duration of 
these movements upon the surface and beneath it have 
been found to about equal 1-78. Besides, these experi- 
ments seemed to result in showing that the effect arising 
from the difference of tension is not altogether to be over- 
looked, for in the first series in question when the tem- 
perature was but 1 8°, the ratio of duration was somewhat 
increased ; that is to say, about 1-87. 
At the beginning of these remarks it was seen that M. 
Marangoni explains the retarded motion of the needle 
upon the solution of soap by the difference existing be- 
tween the tension of the dirty coating and that of the 
liquid beneath. We have also seen that in regard to 
liquids such as water, saline solutions, etc., which also re- 
tard the needle’s movements, he seemed somewhat em- 
barrassed. At the commencement of his work, he insists 
upon the capillary action of the meniscus, then further on, 
he appears to attach but little importance to it, and in- 
vokes a small quantity of dirt ; further on still, he takes 
refuge in M. Van der Mensbrugghe’s theory. 
As far as the capillary action of the meniscus is con- 
cerned, I have endeavored to make it thoroughly under- 
stood that if we admit it at all, we should consider it as 
being probable the very reverse of what M. Marangoni 
supposes. He knows, moreover, that the action of a 
meniscus would not be sufficient in itself to satisfactorily 
explain the existence of any phenomena ; for example, 
it could not account for the rotation of the entire surface 
of the liquid. M. Marangoni, therefore, only ascribes a 
partial role to it, and at the same time seeks protection 
under a coating of dirt and the ideas expressed by M. 
Van der Mensbrugghe. But, you will ask, where then 
does this coating of dirt come from ? Does it arise from 
particles of dust floating about in the atmosphere ? In 
his first work M. Marangoni says that water which has 
1 In order to do this, the pollen must be spread upon the surface of the 
liquid by means of a small paper tube held at a certain distance above the 
solution. Care must be taken to do this as quickly as possible, as the soap 
moistens the particles and causes them to sink rapidly. 
