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|THE STORY OF THE LENS||The Ultramicroscope|
|HO has not seen the countless myriads of glistening dust motes dancing in some stray sunbeam that has found entrance to a darkened room? But how many realize that this very commonplace experience affords a beautiful demonstration of the principle of the ultramicroscope, an instrument that enables the scientist to come|
very close, if not quite, to seeing the molecules of matter? The ordinary
microscope has reached the limits of magnifying power, and without some
new instrument making possible a keener vision and greater depths of
penetration that immense universe of life and matter lying just beyond the
frontiers of the microscopic world would have forever remained a mystery.
But once more the "impossible" has given way before the boldness of the
dreamer, and we find ourselves in the very ante-room of the molecular
and atomic mysteries.
To be seen, an opaque object must either reflect light or be self-luminous. The ordinary microscope employs direct illumination and the opaque object is made visible by the absence of light, due to the light waves which it cuts off. For light produces waves of definite known lengths in the all pervading ether of space. The limit of microscopic vision is determined by the shortest wave length of light perceptible to the human eye. This length is sixteen millionths of an inch, and, therefore, when an object is less than one half that amount the wave simply bends about it, just as a water wave encircles a small obstruction, and reuniting moves forward as though no obstacle had been in its path. Hence we see that it is idle to talk of direct vision microscopes of constantly increasing magnifying power.
The ultramicroscope, however, makes these exceedingly minute particles, too small for direct vision, behave as self luminous bodies. It utilizes an ordinary compound microscope to observe objects placed against a dark background and rendered highly luminous by an intensely bright beam of light at right angles to the line of vision. The first substance to be examined in this way was gold dissolved in ruby glass. A converging pencil of light was made to illuminate the glass and behold, the particles of gold stood forth, glistening points of light, like stars in the Milky Way. Although red when viewed by transmitted light, these particles were now green and they danced to and fro in zig zag paths with a very rapid motion.
Four conditions are requisite for success with the ultramicroscope: (1) An intense source of light; (2) no ray of light
must be allowed to fall upon the eye either directly or by reflection;
(3) a very dark background; (4) the beam of light must be very thin.
Directly beneath the microscope objective is placed the dark background
stage and to one side an arc light and system of lenses. For solutions
a retaining cell is placed upon the stage.
One of its greatest uses has been in the study of micro-organisms that cause disease and are so small that they pass freely through the finest porcelain filters. So-called colloidal solutions, which are really very fine suspensions, have afforded the richest field for the investigator. Since colloidal substances make up the greater part of living tissue, their direct examination is of very great scientific interest and importance. The real nature of the bond between the fiber of fabric and the dyestuff with which it is colored, long a mystery, is revealed by the ultramicroscope. An examination of the blood serum displays countless minute particles hitherto unknown.
But perhaps the greatest service that this new instrument of science has rendered is in the direct confirmation that it gives of the kinetic theory of matter—that is, the theory that the molecules are in a very rapid state of vibration. By its aid we are able actually to see particles that approach very closely to molecular dimensions, and the very rapid motion which they exhibit points to an infinitely more rapid movement on the part of the molecules of the medium in which they are buffeted about. It has often been said that we should never be able to see the molecule but the computed dimensions of the molecules of such organic substances as starch and albumen are well within the limits of the ultramicroscope and actual observation of them is almost an accomplished fact. But the ultramicroscope does not reveal the true appearance of these particles. They seem to be only structureless disks of light like blazing suns rather than planets shining by reflected light, as are the objects of ordinary microscopic vision. The ultramicroscope has broken down one more barrier lying between the truths of the universe and man's incurable yearning to understand them.