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camera lucida. This is a matter of very great importance in the^ 

 rapid production of good camera lucida drawmgs. It olten 

 happens that the hght coming tlirough the mstrument is so famt 

 tiPt it is only by shutting the light quite off from the drawmg 

 that the investigator can see the details of the structures to be 

 sketched. This darkening has in the past been accomplished 

 in various ways. It has for instance been accomplished by hav- 

 ing a pencil on the butt end of which is a feather to be flirted 

 in between the eye and the drawing board so as to oblit- 

 erate the image of the latter. There are other methods of 

 accomplishing the same end. With the foot-power arrange- 

 ment, the light is shut o& or let on without the operator's dis- 

 turbing the position of his body or his drawing-point. More- 

 over, the light can be so modified as to instantly bring about 

 that 'adjustment which is most favorable for any particular part 

 of the sketch. To describe the whole operation briefly, we may 

 say that the operator's left hand rests on the left-hand leg-of- 

 mutton table on a level with the fine adjustment of the micro- 

 scope. His left hand therefore is in a position to work the fine 

 adjustment screw with the greatest ease and facility, and the 

 most careful adjustments of focus can be easily accomplished. 

 His right hand carrying the drawing-point rests on the drawing 

 board and is engaged in the production of the sketch. As the 

 light required for the various portions of the drawing varies he 

 can by a slight movement of his right foot, which in no 

 way disturbs either of his hands, and in no way disturbs 

 the equilibrium of the instruments, effect the desired illu- 

 mination of the drawing. It is found that the drawing 

 surface best adapted to the production of camera lucida 

 drawings is a dark, and, preferably, black surface. On this » 

 surface a white drawing point should be used. For most objects 

 this is a considerable improvement over the ordinary pencil used 

 on white paper, as will be at once admitted by any one who 

 makes a trial. The method found most effective in this labor- 

 atory is that of using a thin black tissue-paper which is blued 

 on the under side. A piece of enameled board of suitable size 

 for the drawing is placed on the drawing board, i. e., the right- 

 hand leg-of-mutton table, and it is then covered with the black 

 tissue-paper with the blue side down. A tracing is now made 

 with a white ivory point. This results in the production of a 

 blue outline drawing on the enameled board. This sketch is put 

 aside for further reference, or for the production of a finished 

 drawing whenever necessary, or may be finished up at once. The 

 object to be secured in this blue sketch is a sufficiently good 

 lepresentation of the object to be illustra'-.ed which sha'.rhave 



