USE OF THE IMAGINATION. 431 
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 
au 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. J 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- pa per. By 
such filtering no freedom from suspended particles is secured. The 
application of a condensed beam to the filtrate renders this at once 
evident. 
\ See " New Chemical Reactions Produced by Light," vol. i. 
