1892.] 



connected ivith Cloudy Condensation. 



421 



The Seat of the Sensitiveness of the Jet. 



The seat of maximum sensitiveness to all influences tending to 

 change the condensation from ordinary to dense is near the origin of 

 the jet close to the nozzle. The different influences, however, affect 

 the jet to different distances from its origin. The most limited in 

 the range of its action is cold, which only produces the dense con- 

 densation when it acts near the nozzle, whereas some of the other 

 influences have some effect, though a gradually decreasing one, to a 

 distance of 2 or 3 cm. from the nozzle. 



The following experiment illustrates the limited range of the 

 action of cold : — A piece of ice about 2 cm. thick was selected, and a 

 small hole bored through it. The ice was then held so that the steam 

 jet passed through the opening. While the ice was held at a distance 

 of 1 cm. from the nozzle, almost no effect was produced, though much 

 cold air from the ice was mixing with the jet. But when the ice w r as 

 brought nearer the origin of the jet, so that the nozzle almost 

 entered the plane of the ice, the dense condensation immediately 

 appeared. 



The range of sensitiveness of the jet to change of condensation by 

 obstructions is also very limited. It is only when the obstruction 

 acts near the nozzle that its effect is great. For instance, the blade 

 of a knife resting on the nozzle, with its back or edge pointing in the 

 direction of the jet, and depressed so as to deflect the jet slightly, 

 causes the jet to become very dense. But if the knife acts on the jet 

 at a distance of only 1 cm. from the nozzle, very little increase in 

 density is produced. 



The range of action of electricity is much greater than that of cold 

 or obstructions. If we screen the nozzle and the part of the jet near 

 it from electrification, it will be found that at a distance of 3 or 4 cm. 

 a slight increase in density can be produced with the electrification 

 used in these experiments. 



The action of the products of combustion has a range similar to 

 that of electricity. If the products are supplied to the jet at a 

 distance of 3 or 4 cm. from the nozzle, a slight increase in thickness 

 can be detected where the impure gases meet the jet ; but the effect 

 is very slight compared with that produced when the gases are taken 

 in at the origin of the jet. 



The limited range of the action of cold is quite what might be 

 expected. Near the nozzle the temperature of the jet is high, and 

 there the drops have no repulsive action ; but at a short distance from 

 the nozzle the temperature is low enough to allow this repulsion to 

 come into action, and the consequence is that any further cooling 

 after the temperature is below a certain point produces little or 

 no effect. It is only when the temperature is above this point that 



