76 Notes concerning the Phenomena 



evident that in the lower segment the currents will converge 

 towards the flame, whilst in the upper segment they will 

 diverge from it. The centres of flame and balance being in 

 a horizontal line, if one end of the balance be above this 

 line, it will be within the currents diverging from the flame, 

 and will consequently be swept away. If below the line, it 

 will be under the influence of currents converging towards 

 the flame, and will therefore be swept to the point nearest 

 the flame, and held there in position. With a source of cold 

 instead of heat, these effects will be reversed. 



"For examining these phenomenain a vacuum, the Sprengel 

 pump used was one constructed by Mr. George Foord, of the 

 Melbourne Mint. It is fitted in a pyramidal frame of wood 

 {see figure), and has a six feet fall tube. The exhaust tube 

 is connected with a T shaped branch, which, in its turn, is 

 joined at one of its extremities to the apparatus containing 

 the balance, the subject of experiment, and at the other with 

 the mercurial gauge. In the cistern of the mercurial gauge 

 is immersed the lower end of a barometer tube, so that gauge 

 and barometer, which are of the same calibre, stand side by 

 side. Over each slides an outer glass tube, graduated to 

 millimetres, which may be raised or lowered so as to allow 

 a pointer of glass, in which the lower ends of these outer 

 tubes terminate, to touch the surface of the mercury. This 

 lower point is the datum line of the graduations. The 

 glass scale tubes are raised and lowered by a very simple 

 mechanism of silk cords, pulleys, and keys of glass, round 

 which the cords are wound, in a manner comparable to the 

 tightening and relaxing of the strings of an ordinary violin. 

 All the junctions of the pump are of stout black indiarubber. 

 The instrument is very effective. 



" The balance employed consisted of a very fine platinum 

 wire with pith-balls at the ends, suspended within a glass 

 bulb, which was connected with the Sprengel pump by its 

 lower extremity (see figure). In constructing this, a bulb 

 is first blown in the centre of a piece of carefully-selected 

 glass tubing. One end of the tube is then drawn out to a 

 point ; towards the other end it is contracted in two places, 

 one to give the indiarubber tubing by which it is to be 

 attached to the Sprengel a better hold, and the other as a 

 preparation for the sealing off*. The little balance is tied by 

 a loop at its centre to a long fibre of cocoon silk, a minute 

 touch of cement being placed on the knot to prevent the 

 silk shifting. The other end of this fibre is tied to a 



