SCIENCE. 
299 
If the outer layer of the liquid should resist the move- 
ment of the magnet from any viscosity of its own, it would 
pucker perceptibly ; moreover, viscous bodies propagate 
motion with difficulty from any distance. 
The coating of dirt imitates closely an elastic body, in- 
asmuch as it tends to return to its primitive state when 
broken ; however, it substitutes, in place of superficial 
vsicosity, superficial elasticity. 
In regard to those liquids of strong expansive force 
which do not produce bubbles, such as water, the 
greater portion of briny solutions, etc., liquids upon whose 
surface a layer of dirt cannot easily be attested, the re- 
tarded movement of the magnet upon the exterior is 
hardly due to the changes which occur in the cavities of 
the meniscus, terminating the magnet at each end, partly, 
also, to the beginning of a layer of dirt, M. Hagen having 
discovered that the surface of water undergoes modifica- 
tions bv exposing the liquid to the air. But the principal 
cause may reasonably be said to be the fact which M. 
Van der Mengsburgghe has so well described, namely, 
that when the surface of any liquid is augmented, or, in 
other words, when any diffusion of the pure exterior takes 
place, a sudden cooling, followed by an increased tension, 
ensues, and, reciprocally, a warmth and decrease of 
tension correspond to any diminution or contraction of 
the surface. 
This then is the main substance of the theory pro- 
posed by M. Marangoni in compensation for mine. Let 
us endeavor to examine it. First of all, it would seem, 
according to h>s doctrine, that it is merely necessary to 
add to any liquid of strong expansive force which 
does not bubble, a drop of another liquid of weak tension 
in order to produce large bubbles from the former. Now 
if a drop of olive oil or spirits of turpentine be placed 
upon distilled water, the liquid will rebel strongly against 
the formation of bubbles. Should the water be covered 
with a thin coating of either of the above mentioned 
liquids, you will find that it bursts in the bowl of the pipe 
before you have even commenced to blow the bubble. 
We must admit therefore, in the first place, that the sup- 
posed coating of dirt must have close connection with the 
liquid beneath it. The author also assigns an additional 
and indispensible cause for the production of bubbles 
which he describes as the superficial elasticity, or in 
other words, the facility with which the dirt spreads itself 
over the liquid, so that the latter is always covered. No- 
thing however, goes to show us that a thin coating of 
olive oil or turpentine does not possess the same elasticity. 
The author, in fact, describes two circumstances in 
which foreign substances produce a coating upon distilled 
water which is more or less effectual. First of all, if the 
pollen of flowers is spread upon the surface and air blown 
from above within an hour or two, the little apertures 
formed will remain for a long time ; but the liquid refuses 
to form bubbles when blown from a pipe or tube. In 
the second place, they can be produced, nevertheless, by 
means of pure distilled water, if the tube is partially filled 
with small particles of camphor. The diameter of these 
bubbles may reach an inch and more. But we can read- 
ily see that these facts are only the beginning of success. 
However, they are in no wise opposed to the theory of 
superficial viscidity, since in both cases the outer layer of 
the water undergoes modifications. 
According to the author, the superficial elasticity is es- 
timated by the difference which exists between the ten- 
sion of the pure surface and that of the dirty surface, and 
he determines this by means of a small apparatus which 
he calls a capillary balance. In his opinion, as we have 
already seen, when a bubble is blown the coating of dirt 
prevents its being broken. In his statement he gives no j 
reason for this but in a preceding work he explains him- j 
self clearly on this point. He says that if the coating of 1 
dirt should become disunited, the excess of tension upon 
the under layer, or in other words, the superficial elas- 
ticity, would instantly close the aperture. Hence the I 
facility for the formation of bubbles, or as the author calls 
it, the pompholygemc power, should decrease with the 
superficial elasticity. Now M. Marangoni is led to the 
conclusion that all causes which tend to diminish this 
elasticity without removing the dirt, render the develop- 
ment of bubbles much easier. Further on, he returns to 
this proposition and says that “ all those conditions which 
diminish this elasticity to the advantage of the plasticity 
increase the pompholygenic force.” If we examine 
closely his ideas, we can understand that an increase of 
plasticity favors considerably the generation of bubbles ; 
but how is it possible that a diminution of elasticity can 
lead to the same result ? 
Let us return to the first of the two facts quoted above. 
The author finds, by means of his capillary balance, that 
the superfine elasticity of the distilled water, covered 
with pollen, may become doubly as great as that found 
in the saponaceous solution. Now, inasmuch as the 
latter produces large bubbles while the former gives none 
at all, it is necessary, according to M. Marangoni’s prop- 
osition that the plasticity of the saponaceous solution 
should be much superior to that of the distilled water, 
which is rather di .'.cult to admit owing to the peculiar 
rigidity of the surface of the former ; indeed there are two 
totally different liquids in question ; nevertheless, the 
author’s statement seems to apply equally to both in 
this case. 
In order to show that the layer of dirt can be accumu- 
lated upon one portion of the surface of a liquid and 
diminished upon another, M. Marangoni describes the 
the following curious experiment. 
He plunges, into a soapy solution, a ring made of iron 
wire about seven and a half inches in diameter and fas- 
tened to the end of a fork which serves as a handle ; 
when the ring is immersed he draws it out again, holding 
it in a horizontal position ; he then raises it until the cate- 
noid wave, which unites it to the surface of the liquid, 
separates into two portions, one of which forms an even 
layer within the ring, while the other produces a spherical 
cavity upon the liquid ; now, if the temperature is low 
enough (from 12 to 14 degrees), this cavity is very hol- 
low, the radius of the base measuring 48 millimetres, 
while the height is only 27. M. Marangoni began this 
experiment four times, always breaking the cavity before 
again immersing the ring, and by this means he obtained 
the maximum of depression in which the depth was ex- 
actly half of the radius of the base. While the ring is 
being raised the circumference, in accordance with which 
the catenoid lamina unites with the surface of the liquid, 
contracts, and as M. Marangoni affirms, condenses the 
coating of dirt on the interior and dilates it on the ex- 
terior. Hence, when the cavity is once formed a diminu- 
tion of tension takes place in the space limited by its 
base, and an increase of tension occurs on the outside ; 
this excess of tension consequently aids the basis of the 
cavity to enlarge, and results in the depth being 
diminished. 
According to my theory, the superficial layer of the 
liquid contracts, as above stated, on the interior of the 
opening, and dilates on the exterior; but its consistency 
does not undergo any modification. The portion which 
contracts forces a part of its molecules into the mass 
beneath, and the dilated portions attract these atoms. 
Now, according to M. Van der Mensbrugghe’s theory 
which I have mentioned already, these effects cannot be 
produced unless a diminution of tension takes place 
within the contracted portion and an augmentation of the 
same in the dilated part. This phenomenon, however, 
can only occur in a very low temperature, and when, in 
consequence, the cavities manifest a certain viscidity. 
When the temperature is notably higher the cavities are 
smaller and their depression less. At 26 degrees hardly 
any effect is visible. The radius of the base at this tem- 
perature was 23 millemetres, and the height 20 ; but I 
have shown that all cavities formed upon the surface of 
