produced by a Fluid in Motion. Ill 



only be observed by very close watching with the eye a short 

 distance from the column. Experiments of this nature are there- 

 fore unsuited for the lecture table. I have, by modifying Pla- 

 teau's experiment, reduced the velocity of a descending fluid to 

 a minimum, so that the separation of a sphere, together with 

 the intermediate thread and the sphere which it produces, can 

 be readily shown as a lecture experiment. 



The mode of effecting this is, to cause the cohesion acting upon 

 the particles of a fluid mass floating in a medium of nearly its 

 own density to slightly preponderate over the gravitating force 

 of the mass, and then, by slowly reducing the density of the 

 medium, to allow gravity to act upon one portion of the mass. 



A tall beaker was filled with a mixture of alcohol and water of 

 the same density as oil : a quantity of oil was then introduced suf- 

 ficient to form a sphere about 35 millimetres in diameter. When 

 the sphere floated perfectly at rest in the centre of the medium, 

 a small quantity of water was added so as to render the medium 

 slightly denser than the oil ; the sphere now rose slowly to the 

 surface, and assumed the form of a hemisphere with its plane 

 surface in contact with the surface of the liquid. On gently 

 warming the alcohol-and-water mixture, the hemisphere length- 

 ened itself until it became a thick cylinder, hemispherical below, 

 and with its upper end in contact with the liquid surface. 

 Then it began to narrow at a point nearly midway between 

 its opposite ends; and this continued until the cylinder was 

 resolved into two masses of oil, separated by a narrow thread. 

 A moment later the two masses suddenly contracted, — the upper 

 one to a very convex plano-convex lens with its plane surface in 

 contact with the liquid surface, the lower one to a nearly perfect 

 sphere, which during its descent to the bottom of the beaker be- 

 came slightly extended, alternately, at right angles to and parallel 

 with the water-surface. The thread of oil which had been drawn 

 out by the weight of the lower mass, being no longer thus re- 

 strained, contracted into a small sphere floating midway between 

 the separated masses of oil. 



Perhaps a more effective mode of showing the experiment is 

 the following. Prepare, as before, a mixture of alcohol and 

 water ; introduce a quantity of oil sufficient to form a sphere from 

 40 to 50 millims. in diameter, and let the density of the mix- 

 ture be such that the sphere floats 20 or 30 millims. below the 

 surface, the entire depth of the liquid being from 175 to 200 

 millims. On heating the mixture the sphere extends itself into 

 an ellipsoid with its major axis at right angles to the liquid sur- 

 face ; it then gradually contracts at a point midway between the 

 ends, until, as in the previous experiment, only a fine thread 

 separates the two larger masses of oil ; rupture then ensues, and 



