THE MEASUREMENT OF MICROSCOPE DRAWINGS. 



213 



In the same manner every division of the line PQ will be half 

 the length of the corresponding division of the line AB. 



The length of a division on the line PQ corresponding to a 

 one-millimetre division on the line AB will be half a millimetre, 

 and will therefore be equal to one micron mxagnified 500 times. 



Thus, the line PQ divided in this manner, with the divisions 

 referred up the sloping lines to the figures along AB, forms a 

 scale by means of which drawings of a magnification of 500 dia- 

 meters can be measured. 



By dividing the line AD into ten parts, and drawing through 



Fig. 2. 



each division a line parallel to AB, ten scales are formed for 

 magnifications 1,000, 900, 800, etc., and it is evident that a scale 

 for any intermediate magnification whatever can be obtained by 

 drawing a line parallel to AB through the appropriate point 

 on AD. For example, the divisions of the line ST, drawn through 

 the point S on AD two centimetres from D, give a scale for a 

 magnification of 200 diameters. 



With this arrangement, however, the scales for magnifications 

 below 100 diameters are inconveniently crowded together in 

 the lower part of the rectangle. This crowding may be obviated 

 by commencing afresh with the line AB, calling it now a scale 

 for 100 diameters' magnification. Each millimetre on AB will 

 then represent 10 microns, and one centimetre on AB will repre- 

 sent 100 microns, or 04 millimetre. The scale represented by the 



