1887.] on Sunlight Colours. 71 



passing through increasing thicknesses of air largely charged with 

 water particles. [The image of a circular diaphragm placed in front 

 of the electric light was thrown on the screen in imitation of the sun, 

 and a cell containing hyposulphite of soda placed in the beam. 

 Hydrochloric acid was then added : as the fine particles of sulphur 

 were formed, the disk of light assumed a yellow tint, and as the 

 decomposition of the hyposulphite progressed, it assumed an orange 

 and finally a deep red tint.] With this experiment I terminate my 

 lecture, hoping that in some degree I have answered the question I 

 propounded at the outset : why the sun is red when seen through 

 a fog. 



[W. DE W. A.] 



