THE CONSTITUTION OF MATTER. 549 



mechanics, now measure without seeing them, or make their existence 

 plain without grasping them ! We may mention some instances 

 which can give us an idea of these. 



According to Tyndall, when very minute solid particles, smaller 

 than the luminous waves, are diffused in a medium traversed by light, 

 the light is decomposed in such a way that the least waves, the blue 

 ones, predominate in the reflected rays, and the largest ones, the red 

 waves, in the transmitted rays. This ingenious physicist thus explains 

 how the blue color of the sky depends and must depend on the ex- 

 istence of solid particles, excessively minute, diffused in infinite quan- 

 tity through the atmosphere. Tyndall is not disinclined to the idea 

 that these imperceptible atoms might very well be no other than those 

 germs of microscopic orgauisms the presence of which in the atmos- 

 phere has been proved by the labors of Pasteur, as well as the part 

 they take in the phenomena of putrefaction and fermentation. The 

 ova of these beings, which are barely visible under the microscope 

 after attaining full development, and of which the number, ascertained 

 by the most decisive evidence, confounds the boldest imagination, 

 these would be the elements of that vital ether, as we have termed it, 

 that dust which gives its lovely blue tint to the vault of the sky. 

 "There exist in the atmosphere," Tyndall says in closing, "particles 

 of matter that elude the microscope and the scales, which do not dis- 

 turb its clearness, and yet are present in it in so immense a multitude 

 that the Hebrew hyperbole of the number of grains of sand on the 

 sea-shore becomes comparatively unmeaning." And to give an idea of 

 the minuteness of these particles, Tyndall adds that they might be 

 condensed till they would all go into a lady's travelling-bag. Mani- 

 festly these particles escape any kind of direct measurement and ob- 

 servation. Their objective reality can no more be demonstrated than 

 that of the particles of ether can be made evident. Yet there are cer- 

 tain facts which aid us to form a clear conception of them. Let us dis- 

 solve a gramme of resin in a hundred times its weight of alcohol, then 

 pour the clear solution into a large flask full of pure water, and shake 

 it briskly. The resin is precipitated in the form of an impalpable and 

 invisible powder, which does not perceptibly cloud the fluid. If, now, 

 we place a black surface behind the flask, and let the light strike it 

 either from above or in front, the liquid appears sky-blue. Yet, if this 

 mixture of water and alcohol filled with resinous dust is examined 

 with the strongest microscope, nothing is seen. The size of the grains 

 of this dust is much less than the ten-thousandth part of ^ of an inch. 

 Moren makes another experiment, proving in a still more surprising 

 way the extreme divisibility of matter : Sulphur and oxygen form a 

 close combination, called by chemists sulphuric-acid gas. It is that 

 colorless and suffocating vapor thrown off when a sulphur-match is 

 burned. Moren confines a certain quantity of this gas in a receiver, 

 places the whole in a dark medium, and sends a bright ray of light 



