154 



Dr. E. Warren. 



A satisfactory general explanation of all the phenomena is found in 

 the view that with a smooth sphere, cohesion is operative in guiding 

 the advancing edge of the liquid sheath which rises over and closely 

 envelops the sphere. If the surface is not rigid (e.g., is dusty), or is 

 rough, then the momentum of the sheath carries it, once for all, away 

 from the surface of the sphere, and the subsequent motion is quite 

 different. The persistence of the remarkable radial ribs or flutings 

 observable in the film that ensheathes a smooth entering sphere is 

 completely explained by the assumption of a viscous drag spreading 

 from the surface of the sphere outwards, and these flutings are always 

 absent from any part of the sheath that has left the sphere. Their 

 presence is an indication that there is no finite slip at the solid 

 surface. 



Experiments made with water mixed with glycerine show that, up 

 to a certain point, the character of the disturbance is but slightly 

 affected by large changes in viscosity. With pure glycerine, however, 

 a thin film of water absorbed from the atmosphere equivalent to a 

 layer ^ mm. thick, was found completely to change the course of a 

 splash, a striking proof of the importance of the initial motion in 

 determining that which is to follow. 



Experiments conducted in vacuo prove that the presence of the air 

 has no noticeable influence on the early course of a splash, but that its 

 » pressure subsequently prevents cavitation of the liquid under what 

 would otherwise be negative pressures. 



The paper concludes with a reference to the remarkable similarity 

 between the splash at the surface of a liquid and that caused at the 

 surface of a hard-steel armour-plate by the impact of a projectile, and 

 with the suggestion that the explanation may be found in the argument 

 of Poynting,* which demands an increase of molecular mobility with 

 increase of pressure. 



" An Observation on Inheritance in Parthenogenesis." By Eenest < 

 Waeken, D.Sc, University College, London. Communicated 

 by Professor W. F. E. Weldon, E.E.S. Eeceived March 22, 

 — Eead May 4, 1899. 



On certain theoretical grounds it has been supposed by Weismann 

 that offspring produced by parthenogenesis exhibit little or no vari- 

 ability. To determine how far this conclusion was warranted by fact, 

 some measurements were made on Daphnia magna (Straus). f 



* Poynting, "Change of State, Solid-Liquid," 'Phil. Mag.,' July, 1881; see 

 also two very important papers by Tresca on the " Flow of Solids," ( Proceedings- 

 of Institution of Mechanical Engineers,' June, 1867, and June, 1878. 



f The measurements were made under the microscope with Zeiss's screw- 

 micrometer. 



