246 



NATURE 



[December 21, 191 1 



It is admitted that many of the refinements which 

 arc referred to here are ot but small use to the man 

 who docs not make himself acquainted with clemen- 

 tary principles of microscopical theory and manipula- 

 tion ; but any worker who intends to wrest from his 

 instrument the best it is capable of yielding and 

 desires to make himself proficient in its use will find 

 that the English microscope must be employed. 



A Defence of the Continental Form. 



The Continental microscopes are of a shorter build 

 than the original English pattern, and are normally 

 supplied with a tube length of i6o mm. (b inches^, 

 while the English tube length normally supplied is 

 250 mm. (10 inches). 



The short Continental microscopes are more con- 

 venient to use on a table of normal height, and, owing 

 to their compactness and portability, are mostly used 

 in laboratories of universities, institutions, &c., in thij 

 country. 



The equipment of these microscopes varies consider- 

 ably, and the better microscopes of the leading makers 

 are fitted with all the modern appliances demanded 

 with an up-to-date fully equipped microscope. 



The stands are often fitted with mechanical stages 

 of exquisite design and large opening, being revolv- 

 able, and having a displacement for the cross motion 

 large enough to allow for searching over an entire 

 slide ; they are very convenient if serial slides are to 

 be examined. Verniers are provided to locate the 

 exact position of the object, thus saving a great deal 

 of time in finding the exact spot noted on any previous 

 day. 



The substage arrangement is of the usual Abbe 

 form, with sliding sleeve to receive either a fixed 

 ordinary Abbe condenser or an achromatic condenser 

 with centring device. 



The iris diaphragm carrier on the substage is of a 

 very ingenious construction, being provided with rack- 

 work to place the iris out of centre, up to a range to 

 meet the extreme margin of a numerical aperture of 

 i'40, and, owing to the iris diaphragm carried being 

 revolvable around the optical axis of the microscope, 

 specimens can be illuminated from any azimuth and 

 obliquity with the greatest ease. 



The recess in the iris diaphragm carrier takes a 

 polariser, also mica films, in a convenient manner 

 should the microscope be used with polarised light. 



The complete substage with condenser is provided 

 with a rack and pinion work, and the best make acts 

 with such precision, having no back-lash whatsoever 

 in the rack and pinion movement, that the fine adjust- 

 ment of the substage is absolutely superfluous. 



The horseshoe foot, provided with three resting 

 points on the extremity of the horseshoe, has been 

 much improved of late in order to ensure great firm- 

 ness of the stand for visual observation. For hori- 

 zontal use, as is the case in photomicrography, the 

 Continental models are chiefly used with a suitably 

 prepared sole plate with levelling screws and clamping 

 device ; this mode has also proved to be of great ser- 

 vice even with the larger tripod stands of best English 

 make. 



The body tube of some of the Continental stands are 

 exceptionally wide in order to allow the use of low- 

 power objectives without cutting down the field, and 

 aiso to avoid internal reflection. 



The fine adjustment is placed near the stage in the 

 inoat convenient position, and is of the greatest sensi- 

 tiveness, an interval on the scale representing a move- 

 ment^ of 2/1000 of a millimetre. The rackwork is 

 sufficiently large to meet even low powers of 4-inch 

 focus. 



All important sliding parts are not sprung but care- 

 NO. 2iqQ. VOL. 88"| 



fully ground in and free from backslash, whicii 

 essential it the microscope is expected to remain in 

 focui>, chiefly with high powers. Sprung motions* 

 however carefully done, are bound to counteract. 



First-class Continental makers do not spare ejt p w>« e 

 in making these carefully ground-in slii'' : irts, 

 and this is the best and surest manner i lee 



a first-class microscope to be steady in fu. u^. >Vilh 

 the cheaper Continental models the sprung sUding 

 sytem is used to some extent, but less accuracy in this 

 motion is required with such microsct^s, which are 

 chiefly designed for low powers. 



For binocular vision, even with oil-immersion len- 

 the Abbe stereoscopic eyepiece of latest form is sinr. 

 unique. 



To sum up the advantage of the Continental mo<i 

 it is only fair to say that the instruments, thou 

 simple in construction, are certainly most efficient : 

 the highest class of research work in microscopy. 



English and Continental Microscopes. 



The average English microscope of the present day 

 is a representation of a simplified instrument of what 

 in former days presented a complicated and massive 

 piece of mechanism. The Continental model, on the 

 other hand, has gradually been evolved from an ex- 

 ceedingly simple design to an efficient and practical 

 instrument better adapted to the requirements of the 

 serious worker than is the typical English model 

 possessing the multiplicity of racks and screws and 

 milled heads so much admired by a certain class of 

 dilettanti. The serious worker in science has not the 

 time to play with the large variety of unn< > 

 fittings embodied in the typical English mic: 

 while the dilettante finds a whole day may b< 

 spent in a variety of manipulations effecting mech. 

 ical and optical adjustments (mainly mechanical) 

 enable him to examine only a few objects, and si 

 a day's work often proves to be more exhaust: 

 physically than mentally. 



The tripod base is more rigid than the typi' 

 Continental "horseshoe" base, but of recent years th. 

 leading Continental makers have so modified t^ 

 "horseshoe" in that the "toes" are spread outwa: 

 and the "heel" prolonged to an extent that the 

 strument is sufficiently rigid for all practical purpo- 

 When using the microscope in the horizontal posit; 

 for photomicrography the tripod base gives greater 

 rigidity when not fixed by screws or clamps to the 

 photographic apparatus, but it is not wise to empi 

 the microscope in photomicrographic work with 

 having it securely clamped to the base plate of tne 

 apparatus, and therefore in this respect the Con- 

 tinental "horseshoe" is equal to the English tripod. 



There are Continental microscopes made with 

 "horseshoes" giving equal rigidity in vertical and 

 horizontal positions to the tripod, and possessing the 

 great advantage of free access to the substage, a 

 fej\ture generally lacking in the typical English model. 



The substage with centring arrangement is rarely 

 met with in Continental models, but instead, centring 

 .•adjustment is provided in the nosepiece, which is un- 

 doubtedly a more accurate method of obtaining optical 

 alignment than by displacing the condenser to suit a 

 change of objective. Indeed in photomicrography the 

 absence of centring screws in the substage means a 

 considerable saving of time and greater accuracy is 

 obtained by employing centring screws, or the Con- 

 tinental objective sliders, attached to the body tube 

 of the microscope. 



.\s regards the stage : at one period the principaf 

 difference existing between the two makes was that 

 the Continental was provided with an attachment 

 giving mechanical motion, while the English mechan- 



