1892.] 



connected ivith Cloudy Condensation. 



413 



It has generally been stated that the effect of the electrification is 

 sudden and marked, that whenever the jet is electrified it at once 

 becomes very dense. This, however, is due to the manner in which 

 the jet has generally been electrified. Some degree of potential is 

 necessary to produce a discharge from the point, and whenever the 

 potential is high enough to cause this, it is sufficient to charge the 

 drops high enough to give rise to a very dense condensation. But if 

 we make the discharging point extremely fine, or assist the discharge 

 by means of a flame, then, we may begin with electricity of a very low 

 potential, and the increase in the density may be made to begin by 

 almost imperceptible degrees and to increase slowly to the dense 

 form by gradually increasing the potential. 



We shall for the present leave the question of the effect of the 

 ordinary and the dense forms of condensation on the light trans- 

 mitted through them, as it will be better discussed after we have 

 considered all the ways in which the jet may be made dense, and we 

 shall now pass on to consider the second of those given in our list. 



2. An Increase in the Number of Bust Nuclei. 



It has been noticed by previous observers that a flame brought 

 near the jet tended to make the condensation dense ; but, in describ- 

 ing the experiments, a confusion has generally been made between 

 the flame and the products of the combustion taking place in the 

 flame. So far as I have been able to observe, flame has no effect on 

 the density of the condensation. Neither a luminous flame nor the 

 flame of a Bunsen burner has any effect so long as the products of 

 combustion are kept away from the jet. But if the products are 

 drawn into the jet, they have a very marked effect either in increas- 

 ing or decreasing the density. If the flame is near and the gases are 

 hot, they make the jet nearly invisible, but if the gases are cooled or 

 are not in great quantity, then they make the jet as dense as if it 

 were electrified. The simplest way of studying this latter effect is to 

 bring the products of combustion to the jet by means of a metal tube 

 2 or 3 cm. in diameter and about j% a metre long. A small flame 

 about -J cm. high, placed below the level of the jet, is used. One 

 end of the tube is kept over the flame while the other can be brought 

 near the nozzle. It will be found that when brought into that 

 position the jet will at once become dense, and when it is removed it 

 will return to its ordinary condition, and become dense again with 

 every return of the impure gases. 



The increase in density in this case is due to the greater number of 

 dust particles in the gases offering a greater number of nuclei for 

 condensation, and the result is a great increase in the number of 

 water particles, and consequent thickening of the condensation, a 



VOL. LI. 2 F 



