THE POWELL AND LE ALAND STAND. 13 



that we will not add a word more. The first-class stands 

 are usually made from harder metal than the cheaper 

 instruments, in which reduction of cost is an important 

 item : this enables the former to wear better, the screws 

 and racks allowing of a great deal of work before they 

 begin to exhibit " backlash." The productions of Messrs. 

 Ross & Co., Messrs. R. and J. Beck, and Messrs. Powell 

 and Lealand deserve to be placed in the highest rank, as 

 microscopes of the first water, and we cannot do better 

 than describe them. 



The two different patterns made by Messrs. Ross, and 

 shown in Figs. 5 and 6, are furnished with an extremely 

 solid foot, which is cast in one piece. The "coarse adjust- 

 ment " may be easily understood from the illustration, and 

 the "fine adjustment" is obtained by the action of a milled 

 head upon a lever which moves the nose-piece, in either 

 case. Both instruments are furnished with a centering and 

 traversing substage, and also with a rotating movement 

 which is worked by a rack and pinion. The stage itself is 

 very complete, the object slide when laid upon it can be 

 instantly secured in position, and the whole stage with the 

 object in situ can be rotated round the optical axis as 

 a centre. The circular motion is graduated, and thus 

 answers many useful purposes. A rectangular motion in 

 two directions can be imparted to the stage by means of 

 two milled heads. 



In the most recent forms of instrument the stage is 

 made very thin (so far as is consistent with steadiness), and 

 the central opening large, so as to admit light of great 

 obliquity, for which purpose the mirror is placed at the end 

 of a jointed arm, so that it may be considerably extended. 



The large best microscope of Messrs. Powell and Lealand 

 is very heavy and massive ; Dr. Lionel Beale speaks of it 

 in high terms of praise. The focussing movement is upon 



