and Laboratory Methods. 



20:; 



entirely. With this arrangement any portion 

 of the field rnay be illuminated, or the illumi- 

 nation rnay be dispensed with entirely. 



Above the mirror attachment is the camera 

 attachment, which allows the camera to be 

 raised and lowered to any point on the po.st 

 and securely clamped. 'J'he front ?.»oard hav- 

 ing been brought into position and the ground 

 glass adjusted, the whole camera may be 

 lowered or raised, or racked entirely out of the 

 way until wanted. 



Accessories. Besides the camera and 

 stand proper there are several accessories that 

 are excellent time savers. 



(\) A Four-Foot Rule, seen in the figure 

 leaning against the camera frame. This rule 

 has marked upon it the exact distance from 

 the glass plate to the front board and to the 

 ground glass for all combinations needed, 

 'i'hus, by using a Zeiss 8x10 series V lens, 

 to enlarge the object two diameters the front 

 board should be lOj^ 

 inches from the glass 

 plate and the ground 

 glass 30 j^ inches ; 

 for making a 'yi', nat- 

 ural size negative the 

 front board should 

 be 18 inches and the 

 ground glass 29 inches, and so on, for other enlargements and reductions. The 

 advantage of this rule is that the camera is adjusted quickly and accurately with- 

 out experimenting. When the specimen is in place the camera may be racked 

 to such position as to bring the highest part of the object Tthat nearest the lens) 

 into sharpest focus. Those who do not use a rule of this kind will find it a sur- 

 prising convenience. If the stand is of a different design it is sometimes prac- 

 ticable to mark these distances upon the post to serve the same purpose. 



(2) A Ruled Card is prepared from a piece of heavy cardboard 30 x 30 

 inches, the size of the glass plate, and ruled so as to have areas corresponding 

 to multiples of different sized plates. Where a large number of plates are used, 

 the cost becomes an item worth considering, and there is no occasion for using 

 an 8x 10 plate if G^/^ x 8j^ or .5 x7 will answer. The areas for the 4x5 and 

 8 X 10 plates are 30 x 24, 2.5 x 20, 20 x 16, 15 xl2, 10 x 8, 5 x 4, and 2i^ x 2. The 

 reverse side of the card is ruled for the 5x7 and 6|4 x 8^ plates. These two 

 sizes do not coincide as is the case with the 4x5 and 8 x 10, so a dotted line is 

 used for the 6^/^ x 8^ fields and a line for the 5 x 7. 



This ruled card serves two purposes : (1) The object is placed upon it to ascer- 



