﻿Coloured Cloudy Condensation. 21 



The two essential appurtenances are the thermometer t, to 

 register the temperature of the inflowing air at C, and the 

 open mercury manometer (not shown) by which the pressure 

 of the steam entering the jet j is measured. Inasmuch as a 

 mercury thermometer is not very quick in its indications, the 

 air at a given temperature must be allowed to pass over the 

 bulb of t for some time before the record is taken. 



The steam used was generated in a copper globe about 

 25 cm. in diameter, and provided with a water-gauge and a 

 steam-gauge. The vessel was heated by a large ring-burner* 

 and is strong enough to withstand, say, ten atmospheres, 

 though in the present work pressures below two atmospheres 

 fully suffice. 



G- and H are forms of air-filters to be described in § 14. 



4. The air entering C is taken out of the atmosphere, the 

 three influx tubes E, D, F passing through the window frame 

 WW, and opening into the air on the outside (Smithsonian 

 Park) as shown at 6, c, d. Valves are inserted into each of 

 these tubes at e, f, h, so that the quantity of air passing 

 through any one of them may be regulated or even quite 

 shut off. In the winter, when the valves are open, the air 

 rushes through the tubes w T ith considerable velocity, even 

 when the jet j is not in action. This velocity increases with 

 the steam-pressure actuating the jet, but can be regulated by 

 shutting off the valves e,f, h partially. 



The tube E is clear, and the air passing through it has the 

 temperature of the atmosphere. The tube D discharges into 

 E and is provided with a drum, containing a coil of thin lead 

 pipe of about 06 cm. calibre. About 20 turns of pipe, each 

 somewhat less than 5 cm. in diameter, in a drum 35 cm. 

 long and somewhat less than 10 cm. in diameter, are more 

 than sufficient. In cold weather steam is passed through 

 the lead pipe. Hence by suitably regulating the valves h 

 and /the air flowing through C may be kept at any desirable 

 temperature ; and as temperatures between 9° and 40° only 

 are needed for the present purposes, this arrangement is quite 

 satisfactory. In the summer time chilled brine or an ex- 

 panding gas circulating through the coil will probably be 

 serviceable. 



The tube F also discharges into E, and is useful for in- 

 creasing the dust-contents of the air entering C. For this 

 purpose a little closed basket of wire gauze, attached to a 

 stein passing through a perforated cork, is inserted into the 

 tubulure k, as shown in the figure. A piece of phosphorus 



* This apparatus, used for other purposes, is shown iu Bulletin U.S. 

 Geolog. Survey, no. 54, p. CO (1889). 



