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A UNIVERSAL SCALE FOR THE IVIEASUREIVIENT OF 

 MICROSCOPE DRAWINGS. 



By F. Addey, B.Sc. 



(Read October 12th, 1920.) 



Figs. 1 and 2. 



It is sometimes necessary, in order to identify a specimen in 

 microscopical work, to measure the length or breadth of an 

 object, and to compare these measurements with those of a 

 drawing or photograph made to some known magnification. 

 The object under observa.tion may be measured either directly 

 by means of a calibrated eye-piece scale, or indirectly by making 

 a drawing of it with the camera lucida, and measuring this 

 drawing by means of a scale formed by marking the divisions 

 of a stage micrometer on a piece of paper, with the camera 

 lucida adjusted as before. If the drawing of the object should 

 happen to be made of the same magnification as the drawing or 

 photograph with which the object has to be compared, the scale 

 is, of course, not required, as dimensions can be compared by 

 direct transference from one drawing to the other by means of 

 a pair of dividers, and they need not actually be known. But 

 in any other case a scale is necessary by which the dimensions 

 of the object shown in the drawing or photograph can be expressed 

 in microns, and so compared with the measurements of the 

 object under observation made by one or other of the methods 

 described. It is, of course, easy to calculate a scale suitable 

 for any particular magnification, but if in the course of any 

 work drawings of many difierent magnifications should be 

 met with, the labour of calculating separately all the different 

 scales required would become somewhat tiresome. 



The following is a description of a simple device by means of 

 which scales for the measurement of drawings and photographs, 

 made to any magnification up to 1,000 diameters, can be at once 

 obtained. It is seldom that drawings are met with of greater 

 magnification than 1,000 diameters ; but if it should be necessary 



JouRN. Q. M. C, Series II.— No. 87. 15 



