1892.] 



connected with Cloudy Condensation. 



415 



I had opened the window of the room where the experiments were 

 being made, and when the fresh air came in, the jet began to behave 

 itself in a most uncertain way. At one moment it was quite steady 

 ordinary condensation, and the next it would conduct itself as if 

 electrically excited. Even after the window was closed it continued 

 to change from the ordinary to the dense form of condensation in a 

 puzzling way. It was first thought that the outer air might be 

 electrified, and tests were accordingly made to see if this were the case. 

 These tests showed that if it were electrified it could be so but slightly, 

 as it did not affect a gold leaf electroscope, which it would require to 

 have done to have produced the increased density observed in the steam 

 jet. Electricity as the solution of the difficulty had, therefore, to be 

 abandoned. The only other influence I could think of as likely to 

 cause the effect was some unknown effect of cold ; I, therefore, took 

 the metal tube which had been used in a previous experiment for 

 conveying the products of combustion from the flame to the jet and 

 cooled it. On now presenting one end of this cold tube to the jet it 

 at once responded, and the condensation became as dense as if a flame 

 had been at the other end of the tube, or as if the jet had been 

 electrified. 



This effect was all the more surprising since there was no great 

 difference between the temperature of the air in the tube and that of 

 the room, not more than 10° F. Some experiments were, therefore, made 

 to find out the temperature at which this change takes place, and to see 

 if it was as sudden as it appeared to be. The jet was supplied with 

 air cooled in a pipe, which was surrounded with water for regulating 

 the temperature of the air. The steam nozzle was placed just inside 

 one end of the pipe and pointing outwards, so that the jet drew its 

 supply of air out of the tube. No very satisfactory results were got 

 with this apparatus. It may, however, be mentioned that when the 

 air was cooled the jet somewhat suddenly became dense, and again 

 became ordinary when the temperature was slightly raised ; but with 

 the apparatus it was difficult to say what the temperature of the air 

 really was when the change took place. 



Another method of studying the effect of temperature on the 

 density was tried with fair success ; the nozzle was fitted to the end 

 of a horizontal pipe, the nozzle also being pointed horizontally. For 

 this experiment a morning was selected when the temperature of the 

 room was low. When the experiments began the temperature was 

 40° F. At this temperature the jet was always dense, and neither 

 electrification nor the products of combustion increased its density. 

 The room was now slowly heated, and the jet watched while the tem- 

 perature rose. Up to a temperature of 46° no change took place, and 

 the jet was not made denser by electricity nor by the products of 

 combustion. But when the temperature rose to 47° the jet began to 



2 p 2 



