NOTE ON MICEOSCOPE MICEOMETEY. 

 By Professor W. M. Thornton, D.Sc. 



Ill the increasing use of the microscope by engineers for the 

 measurement of small objects which cannot be dealt with by usual 

 micrometric methods, the need is occasionally felt of a means of 

 calibrating the eye-piece micrometer. For this purpose- it is convenient 

 to have a scale one centimetre long photographed on a glass slide, and 

 divided into millimetres, half millimetres, tenths, hundredths, and 

 possibly thousandths. 



This is covered with a thin slip of mica or glass cemented on round 

 the edges. 



The object of this note is to call attention to the convenience of 

 the combination of such a scale with a fully divided ocular micrometer 

 as a means of calibrating rapidly and with sufficient accuracy for most 

 purposes, any system of eye-piece and object at any extension, in micro- 

 scopes not fitted with travelling micrometer stages. The idea is no 

 doubt old, but enquiry over a wide area has shown that it is not in 

 use by those making daily observations, and to engineers and physicists 

 who are not in immediate touch with microscope theory and formulae 

 it may be useful to have both a loose scale in the eye-piece and a- 

 graduated slide for calibration. 



Dr, Maurice Langeron, Chief of the Laboratory at the 

 Medical Faculty, Paris, presented the following papers on 

 behalf of Dr R. Bazin. 



MAKING ENLAEGED-SCALE DEA WINGS AFTEE BAZIN. 



The device dispenses with a camera lucida, and consists of an 

 ordinary biconvex lens A, giving a virtual, erect and enla¥ged 

 image of the object 00, which is placed between the lens and its 

 focus; Fig. 1 explains the arrangement. An image of the paper 

 and of the point of the pencil C is formed on the plane on which 

 the object rests, being produced by the plano-convex lens B of 

 short focus; this image is real, reversed and reduced in size, because 

 the paper is at great distance beyond the focus. The biconvex lens 

 A enlarges both the small image of the pencil point and the object 

 itself, which are in the same plane. In drawing one has merely to- 

 trace the outline of the image. 



EYE-PIECE GRATICULE FOE DE AWING, MEASUEING 

 AND COUNTING. 



(Bazin's Rtseau Ocnlaire.) 



When painters wish to copy a picture on a different scale, they 

 divide the photograph of the picture, as well as the canvas on 

 which they are going to paint, into small squares. Each little square 

 is then filled up. 



The reseau oculaire, or eye-piece graticule, consists of a plate 

 on which lines, very fine, yet as distinct as possible, form a system 

 of squares of 1 mm. size. This plate is placed on the diaphragm 

 of the eye-piece. 



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