And yet the waves of red light, measured by the
amount of energy which they carry, are immensely more powerful than the
waves of blue. The blue rays are usually called chemical rays--a
misleading term; for, as Draper and others have taught us, the rays that
produce the grandest chemical effects in nature, by decomposing the
carbonic acid and water which form the nutriment of plants, are not the
blue ones. In regard, however, to the salts of silver, and many other
compounds, the blue rays are the most effectual. How is it then that
weak waves can produce effects which strong waves are incompetent to
produce? This is a feature characteristic of periodic motion. In the
experiment of singing into an open piano already referred to, it is the
accord subsisting between the vibrations of the voice and those of the
string that causes the latter to sound. Were this accord absent, the
intensity of the voice might be quintupled, without producing any
response. But when voice and string are identical in pitch, the
successive impulses add themselves together, and this addition renders
them, in the aggregate, powerful, though individually they may be weak.
It some such fashion the periodic strokes of the smaller ether waves
accumulate, till the atoms on which their timed impulses impinge are
jerked asunder, and what we call chemical decomposition ensues.
Savart was the first to show the influence of musical sounds upon liquid
jets, and I have now to describe an experiment belonging to this class,
which bears upon the present question.
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