1870.] MISCELLANEOUS 361 



MISCELLANEOUS. 



On the Comparative Steadiness of the Ross and the 

 Jackson Microscope-Stands. — In most of the older Micro- 

 scopes the Body was a fixture, and the focal adjustment was 

 obtained by giving motion to the Stage. This plan, however, 

 was very soon abandoned when the improvement of the Micro- 

 scope, in its mechanical as well as its Optical arrangements, 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 modification;;?. 

 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 Eoss 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, with 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 solid Limb, to the 

 lower part of which the Stage is fixed, may with more propriety 

 be distinguished as the Jackson * model ; since it was originally 

 devised by Mr. Jackson, and was thenceforth almost uniformly 

 adopted by the Firm which may be considered as the represen- 

 tative of his ideas. 



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

 obviously preferable mechanic all i/, 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 oppor- 

 tunity of comparing the performance of two instruments, one 

 constructed on the Boss and the other on the Jackson model, 

 under peculiarly trjang 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 



* 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. 



Vol. V. Y No. 3. 



