530 



SCIENTIFIC NEWS. 



[June 8, 1888. 



yawning depths worlds like ours might be poured like 

 marbles into a teacup. These form the sunspots, some 

 of which, on measurement, have been found to have an 

 area of more than 400 millions of square miles. Their 

 depths remain unmeasured. 



Everybody who has watched the eddies in a stream 

 due to irregularities of motion of the water, knows that 

 these eddies whirl downwards, and are surrounded with 

 compensating upheavals of bulging waters. Such is the 

 case with the solar eddies, their surrounding bulge 

 forming the well-known facitloe, billows of flame mea- 

 surable in tens of thousands of miles in length, and 

 thousands in breadth. 



But what must happen to aqueous vapour drawn down 

 by these mighty maelstroms into the hotter depths of 

 the sun's interior ? 



The researches of Deville, Cailletet, Bunsen, and others 

 prove that it must become dissociated by the heat, i.e., 

 again restoied to the condition of an explosive mixture 

 of hydrogen and oxygen in their most explosive 

 proportions, and yet they cannot explode, so long as their 

 temperature exceeds a certain point varying with the pres- 

 sure — about 5,000° Fahr. at our atmospheric pressure, but 

 much higher down in the ardent depths of the sun's 

 interior. Thus they remain in peace below, but when 

 it comes to their turn to be upheaved again as the 

 bulging faculas, thus rising above the general level of 

 the solar photosphere, which constitutes the outline 

 visible to us, the conditions are changed. Now they are 

 free to radiate and develop the mighty chemical 

 energies residing within them, and they rush together 

 with their characteristic violence, the magnitude of 

 which baffles our feeble imaginations when we en- 

 deavour to mentally measure it. If the explosion of a 

 soap-bubble, filled with this mixture of gases, is deafen- 

 ing, what must be that of a quantity amounting to the 

 bulk of a score of our worlds ? I might say a hundred, 

 but that the water-gases are mixed with other gases and 

 metallic vapours which the explosive action of the 

 combining gases flings forth along with the water-vapour 

 formed by their union. 



For reasons which I have not space here to expound, 

 these explosions cannot be instantaneous like that of the 

 gases on our lecture-tables, but must be rocket-like, with 

 continuously increasing projective force up to a certain 

 point. The observed phenomena correspond with this 

 theoretical demand. 



I also abstain from stating my own theory of the 

 cause of the irregularities of the solar rotation, but 

 merely add that they apply not only to our sun, but 

 equally to all the other suns of the universe, i.e., to the 

 stars, provided they have attendant planets like ours. 

 We have only to suppose the conditions producing our 

 solar prominences to be magnified sufficiently, and we 

 get the outblaze of variable and flashing stars, that have 

 presented such difficult celestial puzzles to our astrono- 

 mers. 



— ■►^t»>^E5<f* — 



SPONTANEOUS MOVEMENTS OF CER- 

 TAIN BODIES ON THE SURFACES 

 OF LIQUIDS. 



CAMPHOR, various solid odoriferous bodies, and 

 porous substances saturated with volatile liquids, 

 produce on the surface of water singular movements of 

 rotation and translation. In the earlier half of the 



century these phenomena attracted much attention in the- 

 learned world. They have been ascribed sometimes to 

 electricity, sometimes to the simple mechanical effects of 

 recoil produced by the escape of vapours or fluids 

 emanating from the floating bodies and striking against 

 the air or the water. No definite solution, no clear and 

 satisfactory explanation of the phenomena was given. 



Dutrochet, in order to explain the question, assumed 

 the existence of an unknown force, residing in the sur- 

 face of contact of any two liquors, and named it the 

 " epipolic force." But this notion of a novel force was 

 rejected ; physicists returned, in preference, to an effect of 

 recoil analogous to that of a gun, though every one must 

 have perceived that there was a great disproportion 

 between this cause of motion and the effect produced. 



The idea of Dutrochet was not far wrong. At present 

 it is generally recognised that the surface of a liquid is- 

 the seat of a force known as surface tension. Of this we 

 must endeavour to form a clear notion, as it is essential 

 for an understanding of what has to follow. 



Let us suppose a bubble of soap left at the end of the 

 tube which has been used to inflate it. We see its 

 volume rapidly diminish, and, in fact, disappear. The 

 air is driven out as if by an internal pressure. It is- 

 demonstrated that the force which produces this pressure 

 resides solely upon the free surfaces of the bubble^ 

 whether the inner or the outer. Each surface acts like 

 an extended elastic membrane, which keeps the air under 

 pressure. 



But it is not necessary to have a thin film of liquid with 

 two free surfaces. From our point of view a drop of 

 water is very similar to a soap-bubble, though it has only 

 one free surface, corresponding to the outer surface of the 

 bubble. We may demonstrate that the free and plane- 

 surface of any liquid whatever is also the seat of a force 

 which acts exactly as if the liquid mass was bounded by 

 a very thin membrane, elastic and extended. To this 

 force are due the phenomena of capillarity, and possibly 

 others less well known. It may be added that this 

 surface tension of liquids is in all likelihood merely a 

 special case of the attraction exerted among all bodies. 



But it is very noteworthy that the intensity of this 

 surface tension varies with the nature of the liquid in 

 question. This may be seen on plunging one and the same 

 capillary tube into different liquids, which will ascend to 

 very different levels. To change the surface tension of 

 water it is merely needful to pour upon it a little of 

 some other liquid. The change is almost always a 

 decrease, as the surface tension of water is greater thau 

 that of almost all other liquids. 



M. Devaux, setting out from these fundamental notions, 

 has described in La Nature the little scientific toy repre- 

 sented in Fig. I. This is a boat cut out in thin tin-foil and 

 sloped away at the stern. If the boat is placed upon water 

 it floats easily. A drop of alcohol is then placed upon the 

 stern by means of a pipette, so as just to touch the water, 

 when the boat at once begins to move. At first sight it 

 seems as if a sudden and powerful repulsion was caused 

 by the contact of the water and the alcohol. But let us 

 consider the facts from the point of view of the tensions 

 and the tractions which the boat undergoes when sur- 

 rounded on all sides by a liquid surface. At the prow^ 

 and on the sides this surface is pure water, and is 

 consequently the seat of a strong tension. Behind it is 

 covered with alcohol, and this stratum, though extremely 

 thin, renders the tension decidedly less. Hence, being 

 acted on by two contrary and unequal agencies, the boat 



