564 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



pleasure, all the camerse lucidfe not sending the image in the same 

 direction according to the same angle. It is necessary also that this 

 plane should be able to maintain a fixed position relatively to the 

 Microscope, so that the agreement between the drawing and the micro- 

 scopic image may be i)reserved during the whole process. Such a 

 plane may be made in many different ways. The following is the 

 one which I prefer: — 



Inclined Drawing-board. — This board (fig. 101) is composed (1) of 

 a horizontal part on which the Microscope is placed, (2) of an inclined 

 part on which the drawing is made, and (3) of a bracket, which serves 

 to maintain the inclination of (2). 



The bracket is not fixed to the inclined part, but is carried by a 

 slide, which, guided by grooves, may be pushed more or less under 

 the inclined part, and so raise it. In these movements the bracket 

 passes before a graduated scale at the margin of the board, which indi- 

 cates the degree of inclination obtained. The slide may be completely 

 drawn out of the grooves so as to allow a drawing, the outline of 

 which has been made at the proper degree of inclination, to be com- 

 pleted in a horizontal and more convenient position. Moreover, if it 

 is necessary to refer again to the cameras lucidaB, the slide and the 

 bracket may be replaced exactly in the same position by means of the 

 scale. 



The horizontal part of the board is fixed to the inclined part by 

 hinges, which enables the inclination of the latter to be varied as 

 desired, whilst at the same time keeping it in a constant relation with 

 the Microscope so that the coincidence is maintained between the 

 drawing and the microscopic image. The position in which the draw- 

 ing was made may be easily found again by means of marks. 



The different pieces of this board may be folded upon each other 

 to make it more portable, and when folded it forms a square with 

 sides of about 18 to 20 cm. and 3 cm. in thickness. 



Modified Table of M. EuncJcel d'Herculais. — Where it is necessary 

 to make the drawing at given heights above the table (for the measure- 

 ment of the magnifying power, for instance), I modify slightly the 

 excellent drawing table of M. Kiinckel d'Herculais (fig. 102). 



This is composed of a board resting on a base formed of a double 

 box. The box on which the board is fixed may be raised more or less 

 from the other. Two screws keep it firmly in any given position. The 

 board may thus be more or less elevated as desired. In order to 

 incline the board, all that is necessary is to fix it, by hinges on one of 

 its sides, to the box on which it rests, and then to raise more or less 

 the opposite side by means of a movable bracket or other means. 



4. Determination of the Degree of Inclination. — Whatever may be 

 the apparatus emi^loyed, the important point is to give the appropriate 

 inclination to the plane on which the drawing is made, and to deter- 

 mine this inclination I have employed two processes. 



The first, entirely empirical, consists in laying down on the draw- 

 ing-paper a given length, a micrometric division, for example ; then to 

 modify little by little the inclination of the inclined plane until the 

 division being shifted about in the different points of the field of view 



