Compound-microscope sentence example
Compound Microscope The view held by early opticians, that a compound microscope could never produce such good images as an instrument of the simple type, has proved erroneous; and the principal attention of modern opticians has been directed to the compound instrument.
The development of the compound microscope essentially depends on the improvement of the objective; but no distinct improvement was made in its construction in the two centuries following the discovery.
The excellent manner in which the scales and micrometers are mounted, the employment of a compound microscope for viewing the scales, with its ingeniously arranged and admirably efficient reversing prism, and the perfection of its slow motions for focusing and reading, combine to render this a most accurate and convenient instrument for very refined measures, although too slow for work in which the measures must depend on single pointings in each of two reversed positions of the plate, and where speed of working is essential.
Such an instrument was made as early as 1590 by Zacharias Jansen of Middleburg; and although Galileo discovered, in 1610, a means of adapting his telescope to the examination of minute objects, he did not become acquainted with the compound microscope until 1624 when he saw one of Drebbel's instruments in Rome, and, with characteristic ingenuity, immediately introduced some material improvements into its construction.
The compound microscope generally consists of two positive lens systems, so arranged that the system nearer the object (termed the objective) projects a real enlarged image, which occupies the same place relatively to the second system (the eyepiece or ocular) as does the real object in the simple microscope.Advertisement
Convex glass lenses were first generally used to assist ordinary vision as " spectacles "; and not only were spectacle-makers the first to produce glass magnifiers (or simple microscopes), but by them also the telescope and the compound microscope were first invented.
Antony van Leeuwenhoek appears to be the first to succeed in grinding and polishing lenses of such short focus and perfect figure as to render the simple microscope a better instrument for most purposes than any compound microscope then constructed.
Moreover, this distance between the object and eye is substantially increased in the compound microscope by the stand; the inconveniences, and in certain circumstances also the dangers, to the eye which may arise, for example by warming the object, are also avoided.
For example, the real image may be recorded on a photographic plate; it may be measured; it can be physically altered by polarization, by spectrum analysis of the light employed by absorbing layers, &c. The greatest advantage of the compound microscope is that it represents a larger area, and this much more completely than is possible in the simple form.
In that case, however, in the compound microscope a small object may always be represented by means of wider pencils, one of the foci of the objective (not of the collective system) being near it.Advertisement
If this value of y be inserted in equation (5), we obtain the magnification number of the compound microscope N =tan w"/ tan w =Ol/f i 'f 2 ' =Vl.
The position of the diaphragm limiting the pencils proceeding from the object-points is not constant in the compound microscope.
The older text books called them ' slipper animalcules ' as with careful study under a compound microscope they do look like a slipper.
In 1846 Darwin bought a compound microscope because of his need for higher magnifications (shown left ).
The development of the compound microscope rendered possible the accurate study of their life-histories; and the publication in 1851 of the results of Wilhelm Hofmeister's researches on the comparative embryology of the higher Cryptogamia shed a flood of light on their relationships to each other and to the higher plants, and supplied the basis for the distinction of the great groups Thallophyta, Bryophyta, Pteridophyta and Phanerogamae, the last named including Gymnospermae and Angiospermae.Advertisement