176 



THE POPULAR SCIENCE MONTHLY. 



a drop of soap and water dropping from the end of the fingers spreads 

 out in the basin into the form of a perfect ring that gradually increases 

 as it descends toward the bottom. 



Why do the light particles, instead of scattering promiscuously in 

 the liquid or gaseous medium, take this special state of mobile equi- 

 librium and regular grouping ? Why this form so fragile in appear- 

 ance, instead of any other more simple and possibly more stable ? Is 

 it by pure chance or by pure direction ? And, if the latter is the case, 

 what is the secret of it ? It will not be difficult to detect the secret in 

 a short time, and a few words will show that we have here, not an 

 exceptional and rare case, but a general law of nature, common ex- 

 amples of which exist under our eyes. 



Fio. 1. Wreaths of Tobacco-Smoke. (From Brauwer's picture in the Lacaze Gallery, Louvre.) 



Wreaths of the same shape are often seen to issue from the mouths 

 of cannon when they are fired off ; I have seen them following the 

 locomotive of an express-train. Any one who has pursued a course in 

 chemistry may remember the beautiful experiments in which bubbles 

 of phosphoretted hydrogen take fire spontaneously as they rise to the 

 surface of the basin, and develop superb wreaths of white fumes. 



old Flemish painters, for it recurs under all sorts of forms, either as a detail or as the 

 principal motive in ten, at least, of Tcnicrs's pieces, and in another Brauwer in the gallery 

 at Madrid. 



