SCIENCE. 



301 



regard to this powerful viscidity, relates several experi- 

 ments which make the fact of its existence very percepti- 

 ble. Let us quote the following which is merely the con- 

 tinuation of one I have already drawn attention to : 



A bubble is blown from a moderately wide tube which, 

 however, has a broad mouih, 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. Maiangoni explains this fact by stating that owing to 

 the diminution of the surface, the coating of dirt becomes 

 supei saturated 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: 

 NovV, 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 dirt, 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, th.it 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 ; lout 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- 

 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 siy, 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 , and from 

 M. Marangoni's observations upon the spherical cavities 

 before m mtioned, 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 ot tension is not altogether to be over- 

 looked, for in the first series in question when the tem- 

 perature was but 18°, 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 Mtnsbrugghe. 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. 



