PRACTICAL PHOTO-MICROGRAPHY. 



25 



or with insufficient range of collar correction. In critical 

 work with certain objectives this draw-tube is an' absolute 



FIG. 2. SWIFT'S WALES STAND. 



necessity, and the purchaser of a new outfit is recom mended 

 to insist on a racking draw-tube, which will be found conven- 

 ient in all cases, essential in some. 



