USE OF THE IMA (UNA TION. 43 1 



than the length of a wave of red light. Indeed a first-rate 

 microscope would enable us to discern objects not exceed- 

 ing in diameter the length of the smallest waves of the 

 visible spectrum.* By the microscope, therefore, we can 

 test our particles. If they be as large as the light-waves 

 they will infallibly be seen; and if they be not so seen, it 

 is because they are smaller. Some months ago I placed in 

 the hands of our president a liquid containing Briicke's 

 precipitate. The liquid was milky blue, and Mr. Huxley 

 applied to it his highest microscopic power. He satisfied 

 me that had particles of even one-one-hundred-thousandth of 

 an inch in diameter existed in the liquid, they could not 

 have escaped detection. But no particles were seen. Un- 

 der the microscope the turbid liquid was. not to be distin- 

 guished from distilled water. f 



But we have it in our power to imitate, far more closely 

 than we have hitherto done, the natural conditions of this 

 problem. We can generate, in air, artificial skies, and 

 prove their perfect identity with the natural one, as regards 

 the exhibition of a number of wholly unexpected phenom- 

 ena. By a continuous process of growth, moreover, we 

 are able to connect sky-matter, if I may use the term, with 

 molecular matter on the one side, and with molar matter, 

 or matter in sensible masses, on the other. In illustration 

 of this, I will take an experiment suggested by some of my 

 own researches, and described by M. Morren of Marseilles 

 at the Exeter meeting of the British Association. Sulphur 

 and oxygen combine to form sulphurous acid gas, two 

 atoms of oxygen and one of sulphur constituting the mole- 

 cule of sulphurous acid. It has been recently shown that 

 waves of ether issuing from a strong source, such as the 

 sun or the electric light, are competent to shake asunder 

 the atoms of gaseous molecules. I A chemist would call 

 this, "decomposition" by light; but it behooves us, who 

 are examining the power and function of the imagination, 



* Dallinger and Drysdale have recently measured cilia one-two- 

 hundred-thousandth of an inch in diameter. 1878. 



f Like Dr. Burdon Sanderson's " pyrogen," the particles of mastic 

 passed without sensible hindrance, through filtering-paper. By 

 such filtering no freedom from suspended particles is secured. The 

 application of a condensed beam to the filtrate renders this at once 

 evident. 



t See " New Chemical Reactions Produced by Light," voL L 



