STUDIES OF VORTEX-RINGS. i 77 



Nature herself sometimes produces this phenomenon without any- 

 human intervention, and shows us the vortices of the ignis fatuus, to 

 which the middle ages attached so many poetical legends, rising on 

 summer evenings from the stagnant waters of marshes. The craters 

 of volcanoes also frequently give off smoke in the form of magnificent 

 ring-clouds. 



Huygens observed, with one of the first telescopes, the annular 

 form of those curious satellites of Saturn, the singular equilibrium 

 of which is still a subject of discussion. The periodical November 

 meteors form a real ring of planetary fragments around the earth ; 

 everything seems to prove that the milky way is nothing but a gigantic 

 ring of cosmic dust, of which our sun and its satellites are only a few 

 grains ; the question of the form of the zodiacal light is hardly doubt- 

 ful ; and, finally, among the infant worlds that we call nebula?, the 

 annular figure recurs with such frequency that it can no longer be 

 considered exceptional ; and the inspiration of genius which caused 

 Laplace to see in the fracture of such a ring the whole origin of our 

 solar system is reflected in the broken rings which are found among 

 some of these nebula?. 



The laws of nature, however, frequently reveal themselves best in 

 the infinitely little ; and I have made my first observations toward 

 a new study in watching the filiform currents produced during the 

 osmotic interchange of two liquids through the pores of a membrane.* 



While intimately regarding the curious phenomena with which 

 Ducrochet sought to connect all the laws of life, I devised a way to ob- 

 serve the current of osmose, if I may so speak, in the act. This is not 

 easily done with alcohol or water, but, by carefully taking advantage 

 of the refracting and magnifying properties of cylindrical glasses, I 

 succeeded, at last, in distinguishing before either very dark or very 

 light grounds, slight, thin trains indicative of movement ; and it was 

 really a curious phenomenon to see two liquids of so strong affinities 

 for each other, brought into intimate contact through a permeable 

 membrane, obeying the laws of gravity almost without mixing, and 

 taking their course across each other in the form of distinct threads, 

 which presented at the same time the sharpness and the apparent fixity 

 of a fiber of pure glass. The figure of these threads is not constantly 

 stationary, but is subject to a regular movement, in which periodical- 

 ly, while still preserving its individuality, it seems to undergo alternate 

 swellings and attenuations that give it the appearance from a certain 

 distance of shafts of columns put one upon the other, of larger and 

 larger capitals, or of pointed parasols, or Chinese hats with several 

 crowns. If we look at them from above, we may perceive, in these 

 spirals and expansions, the profiles of real circular rings, slightly 

 attached by an invisible cord to a central stalk which bears them 



* " Etudes sur l'osmose de l'alcool a travers la gutta-percha " (C. R. de l'Assoc. 

 France, Montpellier, 18*79). 

 vol. xx. 12 



