CH. XJ DRAWING FOR MODELS 359 



There is a hand-feed, right-angled arc lamp for small carbons, wiring and 

 connections for the house circuit and a rheostat which will not permit over 6 

 amperes of current to flow. The lamp condenser is in a telescoping tube so 

 that either a parallel or a converging beam of light can be obtained. To avoid 

 stray light the drawing surface is enclosed by a metal box with one side removed. 



A Drawing outfit with the lamp and microscope in line. 



The microscope is supported on a block to give a drawing distance of 254 mm. 

 (10 inches). 



B Drawing outfit with the arc lamp at right angles to the microscope. 



C Drawing outfit with the microscope on an adjustable platform and the 

 arc lamp at right angles with the microscope. 



(3) It must be decided in the beginning how much larger the 

 model is to be than the original object. 



(4) The objective and the drawing surface must be chosen and 

 mutually arranged so that the desired magnification is attained 



( 509)- 



(5) The object must be placed on the stage of the microscope so 

 that the image reflected down upon the drawing surface will be 

 erect, that is, exactly like the object and not inverted in any way 

 (see below 512). 



(6) Each drawing as it is made must be numbered to correspond 

 with the number of the section : This is very important. 



(7) It is desirable to make a duplicate set of drawings, for one 

 set is used up in making the model, and one needs a set for reference. 



The duplicate drawings are easily made by using thin carbon 

 paper as in duplicating writing, or in typewriting. 



(8) Marking the position of the apparatus. If all the draw- 

 ings cannot be made at one time, then the objective, the ocular, 

 if one is used, and the distance of the drawing surface from the 

 tube of the microscope should be carefully measured or indicated 

 by chalk marks, so that when working again exactly the same 

 magnification can be used. It is well also to check up by using the 

 stage micrometer again ( 508). Pictures for models may also be 

 made by photography, (see 542). 



ERECT IMAGES 



512. It has been known from the first use of projection appar- 

 atus that the projected image was inverted, and that this is true 

 whether a simple aperture, a simple lens, or an objective of several 



