84 SUMMARY OF CURRENT RESEARCHES RELATING TO 



which point it may be rapidly lowered free of the guide-post where it 

 may be swung to tbe left, completely out of the path of light from the 

 mirror. When in this position it may be again raised, the guide-post 

 passing through a second hole in the arm and preventing its accidental 

 displacement. 



(3) Illuminating: and other Apparatus. 



Ashe's Camera Lucida.* — D. J. Scourfield describes this accessory, 

 which has been lately slightly modified and thereby improved by its 

 inventor. As will be seen from fig. 5, Ashe's camera lucida is, in 

 essence, an improved form of Beale's neutral tint reflector, the most 

 important difference being that the light from the eye-piece, instead of 



Fig. 5. 



being received directly upon the neutral tint glass, is first of all received 

 upon a small mirror, which reflects the light down upon the neutral tint 

 and so up to the eye. By this means the light undergoes two reflections 

 before reaching the eye, and the most important defect of Beale's neutral 

 tint reflector, viz. the reversal of the top and bottom of the image with- 

 out a corresponding reversal of the sides, is corrected. 



But by making the mirror and the neutral tint glass to rotate upon 

 two parallel pins, the inventor has succeeded in producing a camera 

 which can be used in any position of the Microscope. When the latter 

 is inclined at any angle between about 45° and the horizontal, the image 

 can be projected (only apparently, of course) vertically downwards on to 

 the table by a suitable adjustment of the relative positions of the mirror 

 and neutral tint glass. When the Microscope is vertical (and also when 

 inclined) the image can be projected to the side by rotating the camera 

 90° from its former position. The drawing paper must now be placed 

 on a board inclined at the proper angle, i.e. at right angles to the line 

 of sight. The correct placing of the board is easily determined by ob- 

 serving the outline of the image of the field. If this be a circle, the 



* Journ. Quek. Micr. Club, 1900, pp. 413-0 (1 fig.)- 



