ConJen,<atioii yuch'f proilncfJ ni Air and //>/dro(/eii» 307 

 and less than 1*38, condensation takes place in the tbrin of 

 a shower, called hv him ''Rain-like Condensation." If — 



t^xeeeds 1*38, then dense fogs are produced. i 



J^escription of Apparatus. 



In the course of the experiments, platinum wires of various 

 thicknesses were experimented with. In the earlier ex- 

 periments wires OOG mm. in diameter were used, but as these 

 were so liable to break, owing to the violence of the air- 

 movements when an expansion was made, thicker wires 

 (0"2 mm.) were used in the later experiments. Usually the 

 wire was stretched across a glass bulb, being fastened to 

 thicker pieces of platinum which were fused through the ends 

 of glass tubes joined to the bulb. 



in other cases the thicker leads were both fused through 

 the same tube, and the wire was fastened to them in the form 

 of a loop or spiral. This second method was superior to the 

 first, in that it made it much easier to take out the old wire 

 when necessary and to put in a new one ; but it could only 

 be used for the thicker wires^ as a loop of thin wire soon got 

 twisted up by the rush of air during the expansions. 



The bulb containing the platinum wire was connected to the 

 expansion apparatus by means of a sealing-wax joint. The 

 expansion apparatus used was constructed on the plan 

 adopted by C. T. E. Wilson*. 



It consists of a cylindrical glass tube (PL XL tig. 1), 25 cms. 

 long and 5*5 cms. diameter, in which slides freely a thin-walled 

 glass plunger made out of a Welsbach chimney. The open 

 end of the plunger has been ground smooth and perpendicular 

 to the axis. The outer tube A is tightly wired down on a 

 large rubber stopper, through whjch passes the tube C, of 

 about 1 cm. internal diameter. The greater part of the space 

 beneath the plunger is tilled with distilled water, so that the 

 gas in A is con)pletely cut off from the space between the 

 water-surface and the top of the plunger. The small-bore 

 tube passing through the stopper and closed at the outer end 

 with a pinch-cock is introduced as affording a convenient 

 inlet or outlet for the distilled water. By opening the tap D 

 the plunger rises until the ])ressure of the gas in the bulb is 

 atmospheric (neglecting the weight of the piston). By 

 closing D, and pulling the valve P, the space beneath the 

 })lunger is \mt into communication with the vacuum Y, and 

 the plunger descends with great speed ui)on the rubber 

 stopper, and is there held by the pressure of the gas above it. 



* Phil. Trans. A. vol. cxcii. p. 40o (1899). 

 X2 



