ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
789 
principle, not to be altered during the process of observation, the very 
moment when it was most essential that it should be possible to alter 
it. In later constructions Oberhauser applied a sort of gimbal to the 
forked lever to secure an easier sliding motion to the condenser for 
focusing ; but the system of direct push or pull of the condenser tube 
within the substage socket, with or without gimbal, was always bad, and 
frequently ended in injury to the mechanism. 
Nachet and others improved upon Oberhauser’s arrangement by 
applying under the stage a tail-piece having a dovetail groove in which 
a slide carrying the substage was actuated by a stud-pin and lever 
projecting laterally. 
More recently, and particularly in America, the lever has been omitted 
by many opticians, and the microscopist has had to slide the fitting up 
or down the tail-piece by small knobs on either side. Even the most 
recent student’s Microscope — that of Swift and Son, to which I have above 
referred — has this most inconvenient arrangement. 
It would be too tedious to describe the various other systems that have 
been applied to avoid the expense of the rack-and-pinion. They consist 
generally of some form of screw-action, and probably the best of them is 
now' made by a leading Paris optician,. 
Probably one of the worst focusing arrangements recently designed 
for the substage condenser is that proposed — if not invented — by Mr. 
E. M. Nelson. It consists of a substage socket fixed to the under face 
of the stage ; a spiral slot is cut in the socket, in which a stud-pin on the 
side of the condenser tube moves up or down as this tube is rotated by 
hand. The focal adjustment of the condenser obtained by this motion 
in a spiral direction is very unsatisfactory. I suppose Mr. Nelson 
himself now recognizes its inferiority. 
Until our opticians face the matter by applying the rack-and-pinion 
motion to a fixed tail-piece for students’ Microscopes, I fear we cannot 
credit them with the serious intention of meeting the present require- 
ments of students. It would appear that English makers are constantly 
handicapped by their own desire to supply a superabundance of “ finish” 
in non-eSsentials, to the neglect of much-needed focal and centering sub- 
stage adjustments, which every student would soon learn to appreciate. 
If a beginner now asks the advice of an expert as to the microscopical 
outfit he should obtain, on explaining his requirements to the optician, he 
will probably be met at once with some such statement as follows 
“You can have a substage with rack-and-pinion and centering adjust- 
ments ; but these things are only fitted to the better class of Microscopes 
commencing at the price of £,x ” — the real drift of which is to force the 
student into a larger outlay — to make what is commonly known in busi- 
ness as a “ substantial transaction.” 
The fact seems to be that in England the manufacture of fairly good 
Microscopes is in the hands of so few opticians that they believe they can 
wholly control the trade. It is for responsible teachers in medical 
schools to combine and authoritatively formulate the desiderata of a 
student’s Microscope — the laws of demand and supply will do the rest, 
though they should lead us to engage foreign opticians to drive English 
Microscopes of the students’ class out of the field. Such a course does 
not seem patriotic ; but I fear our opticians are proof against friendly 
