ruling plates covering 224,000 lines per inch, such as would aggregate in superficial areas to over 50,000,000,000 to the square inch! Such minute divisions are wholly beyond the resolving power of the most elaborate of modern microscopic appliances; for it has been shown by Sorby[1] that the ultimate power of the microscope for distinct definition is limited to the examination of magnitudes not less than one-half of the average wave-length of the luminous spectrum; and it is shown, upon the authority of Helmholtz, that when the amplitude of the object is less than this half wave-length—or somewhat in excess of 80,000 to the inch—the dark interference-fringes impair the definition of the instrument, except in the case of striated markings, which may be clearly defined, or resolved, by so arranging the illumination as to mask the fringes, and bring out a good definition even in excess of 100,000 to the inch. Hence, the main difficulty attending the possible amplification of objects less than about the 1100000 of an inch in diameter is a purely physical one, and depends upon the constitution of light itself.
The various phenomena of chemical physics teach us that matter is not homogeneous, but is made up of infinitesimal particles or atoms, the term atom meaning indivisible particle; and that the term molecule—meaning literally a little mass—refers to an aggregation of two or more atoms. Thus, a crystal of common salt may be pulverized until one of its fragments is barely discernible to the highest range of microscopic power, and still this fragment will retain all the characteristics of salt. This same microscopic portion is susceptible of a further subdivision by solution in water, when the spectroscope will detect its presence in the still minuter quantity of the one-hundred-millionth part of a grain. Here, in the case of salt, physical analysis ends, and, aside from chemical analysis, any further subdivision must be by the process of abstraction, until by its means we arrive at the mental conception of a portion so minute as to consist of an atom of sodium united by the bonds of chemical affinity to an atom of chlorine. This is now a molecule of common salt. Any further division destroys the entity of the compound, and results in the decomposition of the salt into the atoms of its elements. Hence a simple molecule is the smallest portion of any chemical compound that is not susceptible of subdivision without destroying its entity, or, in other words, the smallest number of atoms that can cohere to form a compound constitute the molecule of that compound. An atom is designated as the ultimate particle of any elementary body, and is not susceptible of any further division within the range of human analysis.
Were it possible to magnify the atoms of matter to a diameter available for distinct vision, we should be met at the outset by a difficulty too astounding for realization. It is a matter of easy proof
- ↑ H. C. Sorby, F. R. S., in his anniversary address to the Royal Microscopical Society, in the Quarterly Journal of Microscopical Science for April, 1876.
