122 FRAGMENTS OF SCIENCE. 



to the production of the'celestial blue. Now when two 

 vessels are placed before us, each containing sky-mat- 

 ter, it is possible to state with great distinctness which 

 vessel contains the largest particles. The eye is very 

 sensitive to differences of light, when, as in our experi- 

 ments, it is placed in comparative darkness, and the 

 wave-motion thrown against the retina is small. The 

 larger particles declare themselves by the greater white- 

 ness of their scattered light. Call now to mind the 

 observation, 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 per- 

 mitted to act upon a certain vapour. 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 distinctly smaller particles than those sought 

 for in vain by Mr. Huxley. These particles, as already 

 stated, must have been less than Io( i 00o th of an inch 

 in diameter. And now I want you to consider the fol- 

 lowing 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 magni- 

 tude 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 ob- 

 jects of the microscope are literally immense. 



in mass, the vastness in point of number of 



