214 PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 



Th(^ ran^e of action of electricity is inucli greater than tliat of cold 

 or obstnictiou. If we screen the nozzle and tlie part of tlie jet near it 

 from electrification, it will be found that at a distance of 3 or 4 centi- 

 meters a slight increase in density can be produ(:>ed with the electrifi- 

 cation used in tliese 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 centimeters from the nozzle, a sliglit increase in thickness can 

 be detected where tiie 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. IS ear the nozzle the temperature of the jet is high, and there 

 the drops have no repulsive action; but at a short distauee 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 tlie cooling has any 

 iutluence. The same explanation holds good for the limited range of 

 the action of obstructions in front of the jet. 



At a distance of a few centimeters from the nozzle new drops seem 

 still to be forming, as the density of the condensation is slightly increased 

 by increasing the supply of nuclei at that distance. The drops seem 

 also occasionally to coalesce at a distance of 3 or 4 centimeters from the 

 nozzle, as electricity slightly' increases the density of the condensation 

 even at that distance. 



PART II.— COL(3R CONNECTED WITH CLOUDY CONDENSATION. 



In the following remarks it is not intended to discuss the many color 

 phenomena which are known to be connected with cloudy condensa- 

 tion. Attention will be confined princii^aily to some new phenomena, 

 the experimental illustration of which has been developed in the pres- 

 ent investigation. 



Before describing these experiments it may be as well to refer to 

 some changes which take place in the constitution of cloudy condensa- 

 tion, both while it is forming and after it has been developed, as it will 

 be necessary for us to keep certain points in view while discussing the 

 color j)henomena. There are two points to which special refereu(;e is 

 re<piired. These are, first, the manner in which the appearance of the 

 condensation is affected by the greater or less degree of super-satura- 

 tion, that is, by the rate at which the condensation is made to take 

 place; and, second, the changes which take place in the appearance of 

 this cloudy condensation after the tendency for the vapor to deposit has 

 stopped. •• 



These two points may be best discussed by taking the second first. 

 Suppose we blow some steam into the air inside a glass vessel and leave 



1 



