122 FRAGMENTS OF SCIENCE. 



vation, or effort at observation, made by our President, 

 when he failed to distinguish the particles of mastic in 

 Briicke's medium, and when you have done this, please 

 follow me. A beam of light is permitted to act upon 

 a certain rapour. In two minutes the azure appears, 

 but at the end of fifteen minutes it has not ceased to 

 be azure. After fifteen minutes its colour, and some 

 other phenomena, pronounce it to be a blue of dis- 

 tinctly smaller particles than those sought for in vain 

 by Mr. Huxley. These particles, as already stated, 

 must have been less than - L * O th of an inch in dia- 

 meter. And now I want you to consider the following 

 question : Here are particles which have been growing 

 continually for fifteen minutes, and at the end of that 

 time are demonstrably smaller than those which defied 

 the microscope of Mr. Huxley What 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 vastness, without 

 leaving any distinct impression on the mind ; and the 

 magnitudes with which we have here to do, bewilder 

 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 con- 

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

 at scattered points, that the heavenly azure is revealed. 

 To the observer on the summit of Mont Blanc, the blue 

 is as uniform 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 



