SCIENTIFIC USE OF THE IMAGINATION. 145 



light, but by duly strengthening the precipitate you may 

 render the white light of noon as ruby-colored as the sun 

 when seen through Liverpool smoke, or ujoon Alpine hori- 

 zons. I do not, however, point to the gross smoke arising 

 from coal as an illustration of the action of small particles, 

 because such smoke soon absorbs and destroys the waves 

 of blue instead of sending them to the eyes of the observer. 

 These multifarious facts, and numberless others which 

 cannot now be referred to, are explained by reference to 

 the single principle, that where the scattering particles are 

 small in comparison to the size of the waves we have in 

 the reflected light a greater proportion of the smaller 

 waves, and in the transmitted light a greater proportion 

 of the larger waves, than existed in the original white 

 light. The physiological consequence is that in the one 

 light blue is predominant, and in the other light orange 

 or red. And now let us push our inquiries forward. 

 Our best microscopes can readily reveal objects not more 

 than g * h °f an i ncn m diameter. This is less 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 

 submit our particles to an experimental test. If they arc 

 as large as the light-waves they will infallibly be seen : 

 and if they are not seen it is because they are smaller. I 

 placed in the hands of our President a bottle containing 

 Brticke's particles in greater number and coarseness than 

 those examined by Brucke himself. The liquid was a 

 milky blue, and Mr. Huxley applied to it his highest 

 microscopic power. He satisfied me at the time that had 

 particles of even 1 1 6 th of an inch in diameter existed 

 in the liquid they could not have escaped' detection. Bu( 

 no particles were seen. Under the microscope the turbid 

 liquid was not to be distinguished from distilled water. 

 7 



