502 SUMMARY OF CURRENT RESEARCHES. 



'■? The second modification is the blind worked by foot-power (fig. 60, 

 82). The object of this blind is to illuminate the drawing with anv 

 degree of light at an instant's notice, and to do this without in any way 

 disturbing the adjustment of any part of the Microscope or camera- 

 lucida. This is a matter of very great importance in the rapid produc- 

 tion of good camera-lucida drawings. It often happens that the fight 

 coming through the instrument is so faint that it is only by shutting 

 the light quite off from the drawing that the investigator can see the 

 details of the structures to be sketched. With the foot-power arrange- 

 ment, the light is shut off or let on without the operator's disturbing 

 the position of his body or his drawing-point. Moreover, the light can 

 be so modified as to instantly bring about that adjustment which is 

 most favourable 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 adjust- 

 ment of the Microscope. 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 

 illumination of the drawing. It is found that the drawing suface 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 



Explanation of Fig. 61. 



Solar Camera, as used to facilitate the production of illustrations from nega- 

 tives and from transparent objects. 



1, steel girder to left of window affording part of the support to the ordinary 

 camera 3 ; cross-piece supporting camera 3 ; 4, support for camera lucida, same 

 being here represented as attached to an ordinary lens carrier ; 5, vertically ad- 

 justible horizontal platform ; 6, drawing board ; 7, horizontal ways for 6 ; 8, 

 object in position to be drawn natural size; 9, mirror of ordinary camera lucida; 

 10, 11, camera lucida support ; 12, light-tight roller-blind used, when unrolled as 

 a diaphragm for the cone of light from the projector; 13, solar projector set in 

 special window casing near floor ; 14, the negative being projected at 23 ; 15, 15, 

 uprights carrying the adjustable sheet of glass on which the drawing 23 is being 

 produced from the negative ; 14, 16, wooden frame for sheet of glass 18 ; 17, metal 

 braces by which the frame 16 may be clamped at the required angle ; 18, sheet of 

 glass through which, as well as through the paper 22, the image is viewed ; 19, 

 roller blinds to shut off extra light ; 20, 21, sticks to which the drawing paper is 

 attached with drawing tacks, these sticks being easily adjustable under the sand- 

 paper-lined wooden spring-bars 24 ; 22, drawing paper ; 23, image being drawn ; 

 24, wooden bar lined with sandpaper and hinged at 25 and constantly pulled in- 

 ward by a spiral spring at 26, so as to lightly but firmly grip the sticks 20, 21 ; 27, 

 screw legs on which, after the apparatus has been adjusted, it can be raised so as 

 to remain firm during the subsequent operations of focusing and drawing ; 28, one 

 of the four castors on which the whole apparatus is adjustable back and forward 

 on the floor to vary the magnification. 



