212 WALKS AND TALKS. 



ceivable direction like the clouds of home-returning swallows 

 in the dusk of a summer evening. These particles of cos- 

 mical matters these clouds of cosmic dust intervene between 

 us and the sun, and must shut out a large proportion of the 

 solar light and heat. We are told by Professor J. P. 

 Langley that not more than half the sun's radiant force reaches 

 the earth. They tell us the remainder is "absorbed" by the 

 atmosphere and the dust which floats there ; but much of the 

 absorption must be accomplished by the cosmic matter which 

 exists beyond the atmosphere. The absorption thus effected 

 would be still greater to the inhabitants of Venus and Mer- 

 cury, if inhabited ; since cosmic matter must be more accumu- 

 lated in the nearer neighborhood of the sun. Thus the tem- 

 perature on those planets would be lower than their proximity 

 to the sun would lead us to suppose. On the same principle, 

 the solar emanations at Mars or Saturn would be greater than 

 their distances from the sun would lead us to suppose. Who 

 can tell how far these adaptations may go in compensating to 

 other planets for losses due to different distances from the sun ? 



We have seen the meteor ignited in the upper air. We 

 have seen its bright streak vanish while we gazed. The little 

 body was melted it was vaporized. While passing through 

 the space measured by its line, it changed from a cold stone 

 to shining dust, and then a darkened dust left floating in the 

 upper strata of the atmosphere. But though unseen, the me- 

 teoric dust still exists. It now belongs to the earth. It will 

 be wafted to and fro by the winds ; it will come down, after 

 some months, and contribute some new material to the earth. 

 Some of these atoms will fall on the ocean ; most of them 

 will fall there ; and after other months they will settle to the 

 bottom and mingle with the ooze which is there accumulating. 

 You will remember our walk under the sea (Talk X), and the 

 comet-dust which we found. It is an impressive thought. 

 This black particle now resting through an eternity on the 

 midnight-shrouded ocean-bed, shone lately in a star. There 

 are greater changes of fortune than any suffered by us. 



The point which we have reached reveals the boundless 



