430 FRAGMENTS OF 



is established and the chill disappears. Some years ago 

 I witnessed Mr. Hirst experimenting at Zermatfc on the 

 turbid water of the Visp. When kept still for a day or so, 

 the grosser matter sank, but the finer particles remained 

 suspended, and gave a distinctly blue tinge to the water. 

 The bltieness of certain Alpine lakes has been shown to be 

 in part due to this cause. Professor Koscoe has noticed 

 several striking cases of a similar kind. In a very remark- 

 able paper the late Principal Forbes showed that steam 

 issuing from the safety-valve of a locomotive, when favor- 

 ably observed, exhibits at a certain stage of its condensation 

 the colors of the sky. It is blue by reflected light, and 

 orange or red by transmitted light. The same effect, as 

 pointed out by Goethe, is to some extent exhibited by peat- 

 smoke. More than ten years ago, I amused myself by 

 observing, on a calm day at Killarney, the straight smoke- 

 columns rising from the cabin-chimneys. It was easy to 

 project the lower portion of a column against a dark pine, 

 and its upper portion against a bright cloud. The smoke 

 in the former case was blue, being seen mainly by reflected 

 light; in the latter case it was reddish, being seen mainly 

 by transmitted light. Such smoke was not in exactly the 

 condition to give us the glow of the Alps, but it was a step 

 in this direction. Briicke's fine precipitate above referred 

 to looks yellowish by transmitted light; but, by duly 

 strengthening the precipitate, you may render the white 

 light of noon as ruby-colored as the sun, when seen through 

 Liverpool smoke, or upon Alpine horizons. I do not, how- 

 ever, point to the gross smoke arising from coal as an illus- 

 tration of the action of small particles, because such smoke 

 soon absorbs and destroys the waves of blue, instead of 

 sending them to the eyes of the observer. 



These multifarious facts, and numberless others which 

 cannot now be referred to, are explained by reference to 

 the single principle, that, where the scattering particles 

 are small in comparison to the ethereal waves, we have in 

 the reflected light a greater proportion of the smaller waves, 

 and in the transmitted light a greater proportion of the 

 larger waves, than existed in the original white light. The 

 consequence, as regards sensation, is that in the one case 

 blue is predominant, and in the other orange or red. Our 

 best microscopes can readily reveal objects not more than 

 one-fifty-thousandth of an inch in diameter. This is less 



