THE PHOTO-MICKOGKAPHIC CAMEEA 135 



has freedom to rotate on a vertical axis, and when clamped 

 down has no power of motion perpendicularly to that plane. 

 The ends of the three points of support should be rounded, 

 and one of these should be dropped into a shallow conical 

 hole; the apparatus then only has freedom of rotation about 

 this one point. The second point should then be placed in 

 a V-groove set in a position so that the groove runs in a 

 direction away from the centre of the triangle formed by 

 the three feet of the apparatus. The third point of support 

 is on a plane surface. It is clear that any apparatus standing 

 in this manner has no freedom to move, and if it is taken off its 

 base for any purpose, will, on being placed again in its required 

 position, be absolutely in the same place it was in originally. 

 It is very difficult indeed to claim this for many of the methods 

 of supporting apparatus which are now in general use, and 

 although the objections to their designs may to a large extent 

 be overcome by good workmanship, they would never reach the 

 same degree of accuracy that can be obtained by following out 

 this method of the geometric slide and clamp. The various parts 

 of the apparatus made by the writer are shown in Figs. 47 and 

 48 ; and, although the apparatus itself looks somewhat complex, 

 nearly the whole of it has been constructed in an amateur's 

 workshop, and by one who is by no means an expert mechanic. 

 In a simple form of apparatus all that is really necessary is to 

 have a baseboard to support the whole, and two long stiff metal 

 rods on which all the components of the apparatus can slide. 



The camera may be supported at either end on the V- 

 grooves and plain slide, and clamped down as described. For 

 each piece of subsidiary apparatus, and for the microscope, a 

 wood table can be made in the same way to slide on these rods. 

 In the case of the microscope it should be placed on three points 

 as described, so that it always returns exactly to its proper 

 position. Any other apparatus, such as the illuminant or 

 subsidiary collecting-lenses, may be supported on small sliding 

 tables in the same manner, so that every part of the apparatus 

 is adjustable, and can be clamped down in any position. Such 

 an apparatus could be constructed very simply at small cost. 



Fig. 47 b shows the adaptability of the apparatus for photo- 

 graphing large objects, either with ordinary photographic lenses 

 or with low-power microscope objectives. The object-carrier 



