208 PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 



cbaiige from the ordinary to tlie deuse form of condensation in a puz- 

 zling way. It was first tliouglit that outer air nii<;lit be eleetritied, and 

 tests were accordingly made to see if this Avere tlie 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 recpiire 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 aban- 

 doned. The only other influence I could thiidv' 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 of 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 eflect 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. Home 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 appeard 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 pointiiig outwards, so that 

 the jet drew its supply of air out of the tube. Xo very satisiactory 

 results were got with this ai)paratus. It may however be mentioned 

 that when the air was cooled the jet somewhat suddeidy became deuse, 

 and again became ordinary when the temperature was slightly nused; 

 but with the apparatus it was diflicult to say what the temperature of 

 the air really was when the change took i)lace. 



Another method of studying the effect of temperature on the den- 

 sity was tried with fair success. The nozzle was fitted to the end of a 

 horizontal pipe; the nozzle also being pointed horizontally. For this 

 experin.ent a morning was selected when the temperature of the room 

 was low. When the exi)eriments began the temperature was 40^ F. 

 At this tem})erature the jet was always dense, and neither electrifica- 

 tion nor the products of combustion increased its density. The room 

 was now slowly heated, and the jet watched while the temperature 

 rose. Up to a temijerature of 4()0 no change took place, and the jet 

 was uot made denser by electricity nor by the products of combustion. 

 But wheu the temperature rose to 47° the jet began to show signs of 

 clearing. The clearing did not however take place regularly; one 

 moment the jet was dense and the next it Avas ordinary. These fluctua- 

 tions would be duo to the unequal temperature of the air coming to the 

 jet. At one moment the air would be the air of the temperature of 

 the room; the next would be this air slightly heated by the metal pipe 

 and nozzle. So that when the jet drew its sui)ply of air horizontally 

 its condensation was ordinary, and when the air currents in the room 



