**EYEPIECE-MICROMETER** — the device for measurement of microscopic objects. The lake - m represents a glass plate with the scale (fig. 1) engraved on glass. Exist shaped (fig. 1, 1), mesh (fig. 1, 2), contrast (fig. 1, 3), contrast with shading (fig. 1, 4) and other types of scales. The shaped micrometric scale 5 mm long divided into 50 equal parts is most often used.

For measurement of microscopic objects the eye lens of an eyepiece is unscrewed and on a diaphragm of an eyepiece place O. - m divisions down, then screw up an eye lens before obtaining the sharp image of a scale. Focusing of an object is made, watching that images of an object and a scale were visible along with identical degree of sharpness.

By means of the special glass scale placed under a lens — a so-called object micrometer (the price of one division is specified, most often it is equal to 10 microns), determine the size of one division of O. - m. For this purpose define the number of divisions an object micrometer falling on one division of O. - m.

Value of one division of O. - m is equal (in micron):

K * (number of divisions object micrometer / number division an eyepiece micrometer) (micron),

where To — scale interval an object micrometer. So, e.g., at increase by 400 times to 5 divisions of O. - the m corresponds one division an object micrometer (with scale interval of 10 microns). Therefore, at this combination of a lens and an eyepiece (with a constant length of a tube) one division of O. - m is equal 10 * 1/5 i.e. 2 microns. If under these conditions length of the measured object corresponds to 2,5 divisions of O. - m, then the true length of an object is equal to 2,5*2, i.e. 5 microns. The most precisely average size is received as a result of repeated measurements.

For precision measurements use screw O. - m (fig. 2), the measuring line can move to Krom by means of the screw under review along a micrometric scale. Results of measurements count on a scale of a drum of a micrometric head. The size of one scale graduation is calculated in the way stated above.

**Bibliography:** Appelt. Introduction to methods of microscopic examination, the lane with it., page 295, M., 1959; Tim-kov V. D. and D. M Goldfarb. Fundamentals of experimental medical bacteriology, page 54, M., 1958.

*V. A. Zuev.*