THE PLANETS, ARE THEY INHABITED 1 



pulsations, and thereby to convey its intonations to the corres- 

 pondingly susceptible organisation of the ear. Without the 

 atmosphere, therefore, even supposing we could live in its absence, 

 however perfect might be our organs of speech and hearing, we 

 should possess them in vain. Voice we might have, but no word 

 could we utter ; listeners we might be, but no sound could we 

 hear ; endowed with the full powers of hearing and speaking, we 

 should nevertheless be deaf and dumb. 



'Another important manner in which the atmosphere adminis- 

 ters to our convenience is, by diffusing in an agreeable manner 

 the solar light, and mitigating its intensity. In this respect, the 

 atmosphere may be considered as performing in regard to the 

 sun what the imperfect transparency of a ground-glass shade 

 performs for the glare of the lamp. In the absence of an 

 atmosphere, the light of the sun would only illuminate objects 

 on which its direct rays would fall ; we should have no other 

 degrees of light but the glare of intense sunshine, or the most im- 

 penetrable darkness. Shade, there would be none ; the apartment 

 whose casement did not face the sun, at the mid-day would 

 be as at midnight. The presence of a mass of air extending 

 from the surface of the earth upward to a height of more than 

 forty miles, becomes strongly illuminated by the sun. This air 

 reflects the solar light on every object exposed to it, and as it 

 spreads over every part of the earth's surface, it conveys with it 

 the reflected, but greatly mitigated light of the sun. ' 



When the evening sun withdraws its light, the atmosphere 

 continuing to be illuminated by its beams, supplies the gradual 

 declining twilight which terminates in the shade of night. 

 Before it rises, in like manner, the atmosphere is the herald of 

 its coming, and prepares us for its splendour by the grey dawn 

 and increasing intensity of morning twilight. In the absence 

 of an atmosphere, the moment of sunset would be marked 

 by an abrupt and instantaneous transition from the blaze of 

 solar light to the most impenetrable darkness ; and for the same 

 reason, the morning would be characterised by an equally 

 abrupt change from absolute darkness to broad, unmitigated 

 sunshine. 



16 



