SOME SPECIAL PKOCESSES ! ! ' ! 269 



or from below, or from one side, as required. Fig. 74 illustrates 

 the relative position of the various parts. 



The water-bath will require to be of a fairly large size, so that 

 there is a considerable thickness of fluid all round the tube. 

 One may be easily improvised in the manner already described 

 for making up glass cells to contain the fluids for colour- 

 filters (p. 207). 



Between the source of light and the tube a condensing-lens 

 may be placed, but it is advisable to so arrange it that a 

 parallel, or approximately parallel, beam is projected on to the 

 object. In photographing such objects in which there is con- 

 siderable variation both of colour and general appearance, it is 

 very difficult to give clearly defined instructions, and it is always 

 necessary to do a certain amount of preliminary shifting of the 

 illuminant before a satisfactory result is obtained. 



The writer has set up a simple arrangement which may be 

 used for photographing plate- and tube-cultures, and also 

 many other objects of a similar character that may occur 

 from time to time ; in fact, any ordinary object such as a 

 museum specimen may be photographed with ease by its use 

 (Pig. 74). 



It consists essentially of a baseboard, say from three to four 

 feet long and about two feet wide, on one end of which the 

 illuminant A is fixed. The latter is supported in any suitable 

 manner so that it has considerable range of movement in a 

 vertical direction. At a distance of three or four inches in 

 front of the illuminant an opaque black screen B is placed, 

 and this screen must be varied in width to suit the particular 

 object which is being photographed ; in the case of tubes it may 

 be, say, two inches broad, effectively blocking out any direct 

 light that might pass from the illuminant A to the tube G 

 placed in the position as shown in the diagram. On each side 

 of the baseboard, and at about six to nine inches' distance from 

 its centre, brass rods EE are fixed, and both these have freedom 

 to rotate about the centre F. On these rods a plane mirror, 

 about eight by six inches actually a piece of ordinary thin 

 looking-glass is fixed. Each mirror is supported on a boss 

 which is made to slide up and down the tube, and which also 

 allows the mirror to be inclined at any required angle. It is 

 evident therefore that by altering the position of the mirror, 



