On the Ascent of Hollow Glass Bulbs in Liquids. 27 



The crystals are of a brownish colour, and are in parts quite 

 transparent ; the faces have an adamantine lustre ; the specific 

 gravity is 4*552, and approaches that of the specimens of the 

 same mineral from the Ilmen Mountains. 



IV. On the Ascent of Hollow Glass Bulbs in Liquids. 

 By Edmund J. Mills, B.Sc, F.R.S.* 



1. "VTTHEN a hollow glass bulb is detained at some depth 

 ▼ t below the surface of a liquid and then released 

 from its position, it rapidly acquires a sensibly uniform velo- 

 city ; and the motion continues to be characterized by such 

 velocity until the surface is reached or nearly reached, the 

 velocity at that time being much accelerated. The bulb next 

 rises somewhat out of the liquid and then falls ; oscillating 

 thus, until it finally comes to rest under the usual conditions 

 of a floating body. In the present paper I propose to give 

 an account of an experimental investigation which has refer- 

 ence to the stage of uniform velocity. 



2. The bulbs I have generally employed consist of Fig. 1. 

 lead glass, and have, as will be seen in the accom- j? 

 panying figure, a somewhat pyriform shape ; the / \ 

 stalk terminates in a hook, which carries an adjusted \ / 

 glass weight. A few small projections are sealed on \ / 

 to the body of the bulb in order to prevent too close & 

 accidental contact with a wetted boundary. In work- 

 ing with these bulbs, I have always effected the de- 

 pression with a piece of glass tubing, and find that Scale \. 

 after some practice, it is seldom an experiment is lost by lateral 

 divagations of the bulb. It is necessary that all the surfaces 

 be clean. 



I. Change of the Diameter of the Reservoir. 



3. A series of glass cylinders having been selected, their 

 mean diameters between two fixed marks 220 centimetres 

 apart were determined. These marks were ruled at places 

 sufficiently distant from the surface and bottom of the liquid 

 to ensure the uniformity of the motion observed between them. 

 The liquids were first heated a little above the temperature 

 desired for the experiments, then poured into the cylinders ; 

 and these were immersed in a much larger glass vessel con- 

 taining water of very nearly the same temperature. The 



* Communicated by the Physical Society, having- been read at the 

 Meeting on May 14, 1881. 



