SCIENTIFIC USE OF THE IMAGINATION 131 



particles which have been growiog continually for fifteen 

 minutes, and at the end of that time are demonstrably 

 smaller than those which defied the microscope of Mr. 

 Huxley — Wliat must have been the size of these particles at 

 the beginning of their growth? What notion can you form 

 of the magnitude of such particles? The distances of 

 stellar space give us simply a bewildering sense of vast- 

 ness, without leaving any distinct impression on the mind; 

 and the magnitudes with which we have here to do bewil- 

 der us equally in the opposite direction. We are dealing 

 with infinitesimals, compared with which the test objects 

 of the microscope are literally immense. 



Small in mass, the vastness in point of number of the 

 particles of our sky may be inferred from the continuity 

 of its light. It is not in broken patches, nor at scattered 

 points, that the heavenly azure is revealed. To the ob- 

 server on the summit of Mont Blanc, the blue is as uni- 

 form and coherent as if it formed the surface of the most 

 close-grained solid. A marble dome would not exhibit a 

 stricter continuity. And Mr. Glaisher will inform you, 

 that if our hypothetical shell were lifted to twice the 

 height of Mont Blanc above the earth's surface, we should 

 still have the azure overhead. By day this light quenches 

 the stars; even by moonlight it is able to exclude from 

 vision all stars between the fifth and the eleventh magni- 

 tude. It may be likened to a noise, and the feebler stellar 

 radiance to a whisper drowned by the noise. 



What is the nature of the particles which shed this 

 light? The celebrated De la Rive ascribes the haze of 

 the Alps in fine weather to floating organic germs. Now 

 the possible existence of germs in such profusion has been 

 held up as an absurdity. It has been affirmed that they 



