218 PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 



cbauge from blue to a yellowish color, and it does not matter liow the 

 change in the condensation is effected; the color always changes in the 

 same way. We can therefore canse the color in the tube to change 

 by electrifying the jet, by a supply of cold air, by a supply of the prod- 

 ucts of combustion, by increasing the pressure of the steam, and by 

 placing an obstruction in front of the nozzle. When any of these, 

 either separately or combined, comes into action, the change is always 

 in the same direction, and if the color was blue it changes to yellow. 



It may be as well to note here that the yellows produced by most 

 dense forms of condensation are f;ir from line, and can not be compared 

 with the blues. The yellows are not at all unlike the colors occasion- 

 ally seen through smoke or in a thunder cloud. Though this is the 

 case with the dense condensation produced by most of the causes, yet 

 a very line yellow is obtained when high-iiressure steam is used. 



It has been suggested that, because an electrified jet causes the light 

 transmitted through it to be colored of a dark yellow-brown, and as the 

 color seen in thunder clouds is similar, that, therefore, the lurid color of 

 thunder clouds is due to the electrification. From what is stated above 

 it will be seen that electricity is only one of a number of influences 

 which can change the condensation of the steam jet and make the light 

 transmitted through it of a yellow-brown color. Further, there is no 

 evidence to show that electricity has any influence of this nature on 

 the form of condensation taking place in clouds, and we are hardly 

 entitled to expect it to have any such influence, as the conditions under 

 which the steam condenses in a jet are very different from those under 

 which condensation takes place m clouds; and we have seen that elec- 

 tricity has no effect in the nature of the condensation when it takes 

 place in a mixture of hot moist air and cold air. There is still another 

 fiict which points to the same conclusion. If, in the steam jet, the pro- 

 l)ortion of dust, i^ressure, etc., are such as to give an earlier stage than 

 the blue, sui)pose the transmitted light be green, then the electrifica- 

 tion may not change it to yellow, but may only make it blue. At pres- 

 ent it is, therefore, very doubtful whether the electricity in a thunder 

 cloud has anything to do with its color. 



Colors observed in cloudy condensation produced by expansion. — Though 

 previous experiments had made me well acquainted with certain 

 color phenomena, seen when cloudy condensation is produced by the 

 expansion of moist air in a receiver, yet I had never observed any 

 colors in the light transmitted directly through the clouded air, such 

 as are seen in the jet of steam when inclosed in a tube. It seemed 

 extremely probable that the reason for this Avould be, that when the 

 condensation is produced by expansion the process is slow, and the 

 particles will therefore be too few to produce any color effects. In a 

 steam jet the expansion, cooling, and condensation, take i^lace very 

 rapidly, and for that reason the number of water particles formed is 



