The Mechanical Parts of the Microscope

The importance of the sub-stage equipment should be strongly urged since, for the systematic study of an object under the microscope, it is necessary to be able to use several different con ditions of illumination. A well-equipped sub-stage is essential if this is to be carried out conveniently and, in selecting the equip ment for a microscope which is to be used in serious investiga tions, the sub-stage apparatus should receive as much attention as any other part of the instrument.

Accessory Fittings.

For the greater convenience of the mi croscopist, fittings of many varieties have been introduced by different makers. Many of these are devised to enable one object glass to be quickly changed for another, and to minimize the work involved in readjusting the instrument when this is done. The necessity for readjustment arises mainly from minor errors in the mounting of the lenses constituting the object-glass system, or in the mounting of the whole object-glass in the object-glass cell. If critical observation is desired, these errors may necessitate re centring the condenser, or the object-glass, each time one object glass is substituted for another.

Rotating nosepieces which carry two or more object-glasses are among the simplest of these accessory fittings. They are not usually provided with centring adjustments for each object-glass, and only permit of the quick changing of one object-glass for another. Interchangeable object-glass carriers, which slide into or clip on to a nosepiece carried by the body tube, are also used.

Each object-glass is fitted permanently into its own slide or clip piece, and is accurately centred once for all. Each object-glass will then be in correct adjustment, so far as centring is con cerned, as soon as its carrier is pushed or clipped into position. Similar carriers are made for holding sub-stage condensers. Such accessories, though very convenient in use, are not essential parts of the microscope. For fuller descriptions of them the reader must be referred to the catalogues issued by the various micro scope makers.

BIBLIOGRAPHY.-Historical:-Quekett, Practical Treatise on the Use of the Microscope (1855) ; J. Mayall Junr., Cantor Lectures on the Microscope (Royal Society of Arts, 1886). General microscopy:— S. H. Gage, The Microscope and Microscopic Methods (1925) ; J. Hogg, The Microscope (15th ed., 1898) ; W. B. Carpenter, The Micro scope and its Revelations (8th ed. by W. H. Dallinger, Igor) ; Sir A. E. Wright, Principles of Microscopy (1906) ; E. 5. Spitta, Microscopy (2nd ed., 1909) ; C. Beck, The Microscope (1923). Theoretical treatment of the microscope:— M. von Rohr, Die Theorie der optischen Instru mente (1904) ; S. Czapski, Grundziige der Theorie der optischen In strumente (Leipzig, 1904). Technical applications:—R. H. Greaves, Introduction to Microscopic Metallography (1924) ; H. Freundlich, Elements of Colloidal Chemistry (Eng. trans., 1925) ; A. Herzog, Die mikroskopische Untersuchung der Seide and der Kunstseide (1924).