26 



PRACTICAL PHOTO-MICEOGBAPHY. 



These are the stands of which we have some experience or 

 knowledge, but there are doubtless other stands well adapted 

 to our purpose. Many of the so-called Students' Stands are 

 well and strongly made, their low price being due not so much 

 to want of good material and work as to absence of all delicate 

 and perhaps unnecessary mechanism. In particular, the pat- 

 tern of Hartnack appears to us commendable among cheap but 



FIG. 3. BAKER'S "NELSON" STAND. 



good microscope stands. One thing, however, in the cheaper 

 class of stands ought always to be carefully tested before a 

 purchase is made, the fine adjustment must work true and 

 without jerk, deviation or "spring ;" and it must be firm and not 

 " give " in the slightest degree when the tube is at any angle. 

 The long lever adjustment of Powell and Lealand's best stands 

 is considered the acme of perfection, and the differential 

 screw known as " Campbell's " is also very trustworthy when 

 well made. Mr. Swift has lately devised an additional inde- 

 pendent safety spring to be used in conjunction with the 

 Campbell screw fine adjustment. 



