GRAPHICAL METHOD OF DRAWING SPECTRA. 



Comtr'uction of Scale for Map of Spectrum. 



23 



The arrangement shown in fig, 2 has been employed to 

 draw the map-scale^ and found to be an accurate and ex- 

 peditious method. 



Fig. 



AB C D, the drawing-board; E F G H, the drawing-paper; 

 T T^ Stanley's ebony-edged T-square^ resting against the 

 pins ER during the operation; M M, Stanley's ebony-edged 

 set square, which slides along the edge of TT ; S S, Stanley's 

 engine-divided millimetre-scale, connected at one end to 

 the edge of the set square M, by pi us and elastic string 

 N Nj so as to slide with the set square, and have its gradu- 

 ated edge parallel to the edge of T T, and also parallel to the 

 lines KK, K'K', on which the scales have to be constructed; 

 L L, a very fine ink-line at right angles to the edge of the 

 scale, beyond the extremity of the required scale K K, on 

 the right-hand side, to which the divisions of the milli- 

 metre-scale are adjusted by the eye, with the aid of a lens 

 placed on a stand, its axis in a vertical plane through the 

 line L L. A fine adjustment of the line and division is ob- 

 tained by means of the blunt handle of the drawing-pin, 

 used as a lever against the end of the scale, the surface of 

 the board or the paper being the fulcrum. 



