110 Mr. G. P. Rodwell on some Effects 



great accuracy the transformation of a liquid cylinder into iso- 

 lated spheres, and clearly explained the cause of the phenomena 

 observed by Savart. One of the modes of examination adopted 

 by Plateau was to lessen the velocity of a descending liquid jet, 

 so that its resolution into spheres could be watched with greater 

 ease and without the employment of Savart' s strap or a revol- 

 ving mirror. He effected this by causing a stream of oil to flow 

 from a small funnel, through a column of liquid of slightly less 

 density than the oil ; it was then observed that when nearly all 

 the oil had flowed from the funnel (that is to say, when the ve- 

 locity of the effluent stream was least) , the stream did not pre- 

 serve its cylindrical form, but was resolved into spheres. Imme- 

 diately before the separation of a sphere, a fine thread of liquid 

 was seen to be extended between the sphere and the liquid from 

 which it separated; and on the separation of the sphere this thread 

 suddenly contracted into one or two minute spheres. The cause 

 of the small intermediate drops observed by Savart was thus ex- 

 plained. Their formation was afterwards observed by Magnus* 

 in the case of a descending stream of water, his observations 

 being made with a revolving mirror, and also by means of a 

 rapidly rotating disk furnished with a narrow slit through which 

 the stream was viewed. 



Professor Guthrie, in a recent paper " On Drops"t> seems 

 to ignore the existence of the fact that these drops were 

 observed by Savart, Magnus, and Plateau, and accurately 

 investigated by the last-named physicist. a When water," 

 he writes, " falls from glass through air, immediately after the 

 drop separates, a very minute drop is frequently projected up- 

 wards from the upper surface of the drop. 1 have not traced 

 the conditions under which this supplementary drop is formed," 

 &c. Prom the above mode of expression one is led to infer that 

 he was unaware of the previous detection of these supplementary 

 drops. 



The particles of liquid of a descending stream must obviously 

 acquire a very high velocity by the acceleration of gravity ; and 

 it consequently follows that the struggle between cohesion and 

 gravity which takes place below the vena contracta of a descend- 

 ing stream cannot, from the shortness of its duration, be ob- 

 served except by means of a rotating mirror, or by some other 

 appliance for causing a body in motion to appear to the eye to 

 be at rest. Plateau's column of oil can be readily observed to 

 transform itself into isolated spheres ; but the production of the 

 thread and its subsequent contraction into a small sphere can 



* " Hydraulic Researches/' part 2, Poggendorff's Annalen, vol. cvi. 

 Translated in the Philosophical Magazine for September 1859. 

 t Proceedings of the Royal Society for July 1864. 



