358 RECORD OF SCIENCE FOR 1887 AND 1888. 



lished the account of some carefully executed experiments on vortices 

 and other motions in water, illustrating points in the movements in the 

 air. 



(5) CoUadon and Weyher. — As to experimental work in circular vor- 

 tices nothing has been more interesting than that done on a large scale 

 in 1887 by CoUadon at Geneva, and Weyher at Paris. 



Coliadon used a simple apparatus for producing vortices and arti- 

 ficial whirlwinds and water-spouts both in water and in air. A more 

 effective apparatus was constructed by Weyher, in which a great variety 

 of interesting vortical phenomena were produced, illustrating what 

 might happen in the free atmosphere if only the conditions were the 

 same. He established a drum, rapidly revolving about a vertical axis, 

 which therefore set in motion the surrounding air of the room or other 

 inclosure. If the drum is at the top of the iuclosure, the air thrown 

 out from it descends along the sides of the room, while, in the center im- 

 mediately below the drum, a rapid spiral or corkscrew movement exists 

 inward and upward. Water contained iu a vessel in the middle of the 

 room is set in motion by the air, and some drops are even carried up- 

 ward through the ascending core, thus approximately imitating the 

 lower end of a water-spout, and showing how spouts and tornadoes 

 originating iu the clouds settle downwards to the earth. Many modi- 

 fications of his apparatus have been made by Weyher, illustrating many 

 problems iu vortex motion, aiul which are valuable for the comparison 

 with the analytical formulie of hydro-dynamics, but which have only 

 indirect bearing on meteorological phenomena. They, however, serve 

 to remove from the mind any difiQculties that may have been experienced 

 by those who hesitate to admit the importance of vortex motion in 

 meteorology. 



(6) Reynolds. — Among the investigations into the motions of fluids, 

 that made by Prof. Osborne Keynolds, on " the two modes of mo- 

 tion of water," has had a peculiar interest for me and seems generally to 

 be regarded as one that has contributed decidedly to our knowledge of 

 the conditions under which steady motion and eddying or vortex and 

 wave motions take place. Reynolds's paper is published iu the London 

 Philosophical Transactions of 1883. In his annual address, November 

 30, 1888, Professor Stokes says of it: "The dimensions of the terms iu 

 the equations of motion of a fluid, when viscosity is taken into account, 

 involve, as has been previously pointed out, the conditions of dynamical 

 similarity iu geometrically similar systems in which the motion is regu- 

 lar; but when the motion becomes eddjing it seemed no longer to be 

 amenable to matnematical treatment. But Professor Reynolds has 

 shown that the same conditions of similarity hold good as to the aver- 

 age effect even when the motion is of the eddying kind ; and moreover 

 that if in one system the motion is on the border between steady and 

 eddying, in another system it will also be on the border, provided this 

 system satisfies the above conditions of dynamical as well as geometri- 



