EULOGY ON ARTHUR AUGUSTE DE LA RIVE. 199 



alone, for some time, remains illuminated, and, suddenly, while the rest 

 of earth sinks into deei)er shadow, takes a bright orange tint, sometimes 

 a bloody or fiery red, and appears like an immense meteor, fixed, incandes- 

 cent, ijot belonging to earth, but suspended in the sky. Soon the ever- 

 increasing shade invades even this icy pinnacle. Its outlines grow indis- 

 tinct, and its color fades to a cadaverous hue. Like the change from 

 life to death in the human fiice is this rapid transformation from the 

 brilliant tints of departing day to the livid tone which follows upon the 

 forehead of this giant of rock and snow. No one can witness the 

 solemn spectacle for the first time without profound emotion ; and the 

 instinctive silence that falls upon the spectator is like the prelude to a 

 prayer. As he turns sorrowfully away, and asks if all is over, suddenly, 

 as if in answer, the mountain is colored anew with a pale rose tint, 

 the reflection of its former splendor. Is the colossus about to revive? 

 No ; this fugitive tint is soon effaced, and darkness covers the scene. 



The rosy glow, the day's farewell to the snow-clad peaks of these high 

 mountains, is only the reproduction in a particular form of the general 

 effects of the setting sun upon clouds. But what is the cause of. the second 

 coloration ? Our associate, after many observations of the summit of Mont 

 Blanc, most frequently subjected to the phenomenon, attributed it to the 

 reflection of the last red rays from vaporous strata accumulated in the up- 

 per regions of the atmosphere. He studied the nature of these vapors, and 

 invented an apparatus for measuring the variations in the transparency 

 of the atmosphere, which are closely observed by the mountaineers, as they 

 judge from them what weather to expect. If the air is perfectly clear, and 

 distant objects plainly visible,the mountains seeming close to the observer, 

 and the sky of a deep-blue color, they will tell you that rain is near, 

 though there may be no other sign of its approach. If the weather is 

 decidedly fine, the air is not perfectly clear, but is pervaded by a bluish 

 vapor, the sky is moderately blue, and mountains seem far away. 



Auguste De La Eive supposed that these vapors, characteristic of 

 fine weather, were composed of mineral and organic particles, whicli 

 float in the air as long as they are dry, but fall to the ground when sur- 

 charged with moisture. They are so abundant, that they take from the 

 air its transparency, which is restored when they disappear. The in- 

 sects which buzz about us are governed by the same law. If the swal- 

 lows fly close to the ground at the approach of rain, and high up in tbe 

 air in fine weather, it is because in the first case the insects upon which 

 they feed are weighed down by moisture, while, in the second, relieved 

 of this burden, they mount higher into space. 



The ardor of Auguste De La Eive for the study of electricity could not 

 be satisfied with only the labors of the laboratory. He conceived the plan 

 of a work which would make known all the results obtained in every 

 branch of this department of physics. Familiar with every science, 

 and speaking all languages, he hoped, by uniting and tracing to their 

 source the materials scattered through the periodicals of different coun- 



