jZ'ual, a1^T,T?o.'] -Royal Microscoincal Socidtj. 183 



III. — On the Comparative Steadiness of the Boss and the Jackson 

 Microscope-stands. By W. B. Caepentee, M.D., F.K.S. 



(Bead iefore the Eoyal Microscopical Society, March 9, 1870.) 



In most of tlie older Microscopes the Body was a fixture, and the 

 focal adjiistmeut was obtained by giving motion to the Stage. This 

 plan, however, was very soon abandoned when the improvement of 

 the Microscope, in its Mechanical as well as its Optical arrange- 

 ments, was seriously taken in hand by men of real constructive 

 ability; and the Stage being made a fixture, two different modes 

 were adopted for supporting and giving motion to the Body, of one 

 or the other of which nearly all the different patterns devised by 

 our now numerous Makers may be regarded as modifications. The 

 one in which the Body is attached at its base only to a transverse 

 Arm, borne on the summit of a racked Stem, I have elsewhere 

 termed the Boss model ; not because Mr. Boss could in any sense 

 be considered its inventor, but merely because he was among the 

 first to employ it, and his original patterns are now in general use 

 vnth extremely little modification. The other, in which the Body, 

 having the rack attached to it, is supported for a great part of 

 its length on a sold Limb, to the lower part of which the Stage is 

 fixed, may with more jDropriety be distinguished as the JaeJcson* 

 model; since it was originally devised by Mr. Jackson, and was 

 thenceforth almost uniformly adopted by the Fu^m which may be 

 considered as the representative of his ideas. 



It has always appeared to me that the Jackson model is so 

 obviously preferable mechanically, that if it had been introduced 

 before the Boss model had come into use, it would have been the 

 one more generally adopted ; and having lately had an opportunity 

 of comparing the performance of two instruments, one constructed 

 on the Boss and the other on the Jackson model, under peculiarly 

 trying circumstances, and having found my previous opinion most 

 fully confirmed, I have thought it well to bring my experience in 

 this matter before those whom it most especially concerns, namely, 

 Microscope-Makers and practical Microscopists. In order that the 

 bearing of that experience may be rightly understood, it will be 

 desirable in the first instance to examine the conditions on which 

 tremor of the Microscopic image depends. 



When the building in which the Microscopist is at work is 

 thrown into vibration as a whole, as by the passage of a heavily- 

 laden cart in the street outside, — or the floor of the room in which 

 he is seated is made to vibrate by the tread of a person crossing it, — 

 the Microscope and the observer move together ; and if the frame 



* In the last edition of my ' Microscope ' I inadvertently designated this as 

 the Lister model, having supposed it to have been devised by Mr. J. J. Lister. 



