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(A critique of the stands built by the major American makers in the late 1870's. Dr. Smith was a prominent microscopist, who contributed, in his own right, to the development of the Acme microscope, built by Sidle and Poulk.)
|Zentmayer||Robert B. Tolles||Bausch & Lomb||W.H. Bulloch|
The swinging sub-stage, which carries the condenser or other illuminating apparatus, including the mirror, swings around a pivot, the axis of which passes through the object observed, so that this object is in every position in the focus of illumination. The stage may be detached with facility, and replaced by one constructed for oblique illumination; the swinging illuminator may then (i.e., with the last-named stage) be used for illumination from above.
The sub-stage is provided with a graduated circle for indicating the degree of obliquity.
An object placed on the stage being in a plane with the axis of the trunnions, it is obvious that if the instrument is placed in a horizontal position, the object is in the axis of revolution of the graduated platform, and the angular aperture of an objective focused on this object can easily be measured. It is equally obvious that in this position the object is in the centre of all the revolving parts of the instrument, to wit, the re- volving stage, swinging sub-stage, and the platform.
The principal stage is similar to the circular one previously used on the “Grand American“; it is provided with adjusting screws for accurate centring, and revolves in a large outside ring, giving facilities for oblique illumination up to 70 degrees from axis (140 degrees aperture), while the graduations serve as a goniometer for the measurement of crystals, etc.
The sub-stage is divided into two cylindrical receivers, to facilitate the adaptation of several accessories at one and the same time; the lower cylinder can be moved up and down or entirely removed.
The fine adjustment (in all other instruments of the Jackson model being in front of the body) is removed to the more stable part of the stand. The bar is provided with two slides, one for the rack and pinion movement, and close to it another one of nearly the same length for the fine adjustment, moved by a lever concealed in the bent arm of the bar, and acted on by a micrometer screw. Thus the body is not touched when using the fine adjustment, and the relative distances of objective, binocular prism and eye-piece remain Unchanged.
The smaller stage of the American Centennial Stand is also provided with screws for accurate centring; this stage is three inches in diameter and extremely thin, allowing, in connection with the swinging sub-stage and mirror, not only the greatest obliquity of illumination, but the mirror and achromatic condenser will rise above the stage when required, as in the case of sunlight illumination, that of opaque objects, etc.
The diameter of the sub-stage is the same as that of the “Grand American"; the accessories of that stand are therefore interchangeable.
As to the general character of Mr. Zentmayer’s work, the author can affirm with confidence that it is not excelled in any particular. The stand just described is beautiful in design, is nicely proportioned, and in every repect reliable and durable. It will stand all of the tests named in the preceding pages. Those wishing a first-class stand cannot fail to be satisfied with the Centennial.
The swinging sub-stage carrying the mirror, etc., is a most valuable improvement, and one that the observer can hardly afford to be without; the mechanism, too, by which this end is accomplished is of the strongest and most workman-like order.
Attention also is invited to the method of attachment of the stage. The latter is solidly held in position, or can in a moment be detached, and another stage substituted.
It has occurred to the writer that the “principal stage” mentioned might very well be dispensed with; the smaller stage being quite sufficient. Possibly a large and plain stage might at times be found a convenience, this could easily be substituted for the more expensive one furnished with the instrument.
As to the smaller stage referred to, the author can “speak by the card.” He had used one of Mr. Zentmayer’s army hospital stands for years, and the instrument gave him good satisfaction. Two years ago, however, desiring a thinner and a revolving stage, he begged Mr. Zentmayer to devise one and fit the same to his stand. Quite a correspondence ensued, and the army stand was thus equipped, the new stage being practically the same as the small one furnished with the Centennial. It worked nicely, and was, in truth, all that the author desired.
In the change of stages proposed, attention is called to the fact that the smaller stage has not the graduated edge. This to the majority of users would not be a serious objection, while, on the contrary, many would gladly avoid the cost of the graduated circle.
Mr. Zentmayer makes some eight or nine different forms of stands. We have room to describe only one other, viz.:
The entire instrument is made of brass, the base and uprights are one piece, of a peculiar shape, and of great rigidity, to which the bell-metal bar is attached by a joint, allowing the use of the instrument at any angle of inclination; perpendicular and horizontal positions are indicated by stops; the coarse adjustment is accomplished by a sliding tube, the tube being but five and one-half inches long, but capable of elongation to the standard length.
The fine adjustment is similar to that of the Centennial — a concealed lever moving the entire body; this adjustment is reliable and very delicate. The sub-stage, plane and concave mirrors, swing in the same manner as do those of the Centennial, having the object in its centre, even when swung over the stage.
The sub-stage carries the diaphragms, of which three are furnished with the instrument. Any piece of sub stage apparatus, such as condensers, paraboloids, prisms, in fact anything from the lists, can legitimately be adapted to the sub-stage, or the same can be instantly removed, with the mirror also, if desired, thus leaving the stand free from any obstruction below the stage.
The sub-stage slides up and down in strong dovetailed grooves, and has centering adjustments by hand. The weight of this little stand I judge to be about three or four pounds; it can, on a pinch, be carried in one’s great-coat pocket.
It is worthy of mention in connection with these two stands of Mr. Zentmayer's, that the fine adjustment has been removed from the front to the rear, or, as Mr. Zentmayer says, “to the more stable part of the instrument.” The author, when his attention was first called to these stands, regarded this change of the fine adjustment as one of doubtfull utility; and he once made the remark to a friend, that should he purchase a Centennial, he should insist that the maker furnish a fine adjustment, both front and rear.
Certain it is that, in the process of correcting a firstclass wide-angled objective, it is a convenience to have the fine adjustment at the front. It is, however, exceedingly difficult to so accurately fit the sliding nosepiece that it shall move up and down with perfect freedom when acted upon by the fine screw, and at the same time to be free from lateral motion, and this lateral motion constitutes a first-class fault to which the attention of the reader has been called on another page. The very best makers have found it difficult to steer clear of this. The writer once met with one of Mr. Zentmayer’s larger stands exhibiting this defect in a marked degree. His own “Grand American Stand" however, in this respect, is faultless.
Thus it will be seen that, in the nature of things, a really fine adjustment acting on the nose-piece involves skilled labor, and this, in turn, involves cost.
Again, the movable nose-piece necessarily changes the length of the body-tube, and this, in turn, again, changes the amplifying power of the objectives, and to get rid of this is indeed “a consummation devoutly to be wished.”
Having had the little Histological in constant use, i. e., from six to ten hours daily, I am now prepared, from my own experience, to state that I am quite well satisfied with the fine adjustment as placed by the maker. It would probably take me a trifle longer to adjust nicely an objective on the Histological, and but a trifle; while, on the other hand, all the objections connected with the adjustment at the nose-piece are avoided.
The Histological, as furnished by the maker, has simply a plain stage with spring-clips. This defect did not pass unnoticed by the writer, Mr. Zentmayer responding promptly to his request with the improvised stage described on a preceding page.
It remains to be noticed that the histological has neither rack nor pinion, and that the coarse adjustment is effected by sliding the body within an adjustable “jacket”. There is no novelty in this, for the sliding tube is “as old as the hills”, and has been extensively adopted in the construction of cheap stands.
The author felt very much like kicking at this feature of the Histological. In a little time, however, experience taught him that the sacrifice of the rack and pinion was not such a serious matter as might be supposed. The sliding movement of the body tube within its jacket in the little stand is very smooth, regular, and reliable, while, on the other hand, there are some advantages accruing to the slide that are not to be obtained by the use of the rack and pinion.
For example: suppose we are working over wet preparations, and unfortunately the front of the objective becomes immersed in the liquid — a misfortune liable to occur daily. It is then, in such cases, a positive convenience to be able to pull the body-tube out of the jacket, cleanse the objective, and return to its place. All this can be done in much less time than would be required, were the instrument furnished with rack and pinion, to unscrew the lens, cleanse, and screw in place again.
The greatest objection that the writer has to urge against the histological stand is this: When it is placed in a vertical position, there is a liability of its tipping forward. This can be prevented by clamping the instrument to the table with a small iron clamp, such as are used by carriage-builders and are sold at the hardware shops for a dime. In this simple way the stand is rendered as solid, more stable indeed than those of the heaviest build.
One of my correspondents, to whom I had stated the above-mentioned objection, informs me that Mr. Zentmayer has made some changes in the foot, securing thereby greater steadiness.
Previous to the introduction of the Histological, it was generally taken and accepted that the purchaser of a cheap stand ought not, in the nature of things, to expect an instrument capable of all work. To a slight extent, and to a slight extent only, does the remark hold good to-day, for the Histological has not the revolving platform, for the measurement of angular apertures (apertures can, however, be measured on the stand), nor has it the circular graduated stage; nevertheless, the Histological will accomplish a larger variety of work than can be performed on the “Grand American Stand” of the same maker, and this, too, be the character of the work what it may, be it the study of a Histological object or the display of the No. 20 of the Moller plate, or the 19th band of Kobert.
As may be arrived at by the tenor of the preceding remarks, the author regards the introduction of the histological as marking an era in the progress of microscope stands. The long-sought problem has been solved, and in the Histological we have a cheap, reliable, and universal stand, suitable for almost any work which may be required, and capable of carrying any and all of the various accessories which in the past have been supposed to pertain only to the heavier and (so-called) first-class instruments.
Furthermore, the author desires in this place to put on record his unfaltering opinion that, in the devising, construction, and introduction of the Histological stand, the maker has bestowed a greater boon on the “body corporate” of microscopists than has been accomplished by others, either at home or abroad. If there be an error in this statement, “time, with its revenges, will set it forth.”
It has rack and pinion for coarse and micrometer screw for fine adjustment, the latter being placed in front of the body, as has been usual in first-class instruments, On the Jackson model. It is furnished with graduated draw-tube; sub-stage with rack and pinion, and centering screws for accessory apparatus; plane and concave mirrors on double-jointed arm; Tolles’ thin stage, admitting light of great obliquity; with rectangular movements by screw and rack and pinion, and rotation on the optical axis of about 270°.
Mr. Tolles makes a modification of this sized stand, the stage being carried by friction rollers, and having entire rotation on the optical axis. The cost of the instrument is thereby somewhat enhanced.
Either of the two stands named, made by Mr. Tolles, may be unhesitatingly pronounced first-class. The workmanship is of the very highest order; the circular stage can be so nicely adjusted as to allow of an entire revolution, under a one-twenty-fifth objective, without the object being sensibly displaced. Either form of stand can be fitted with radial arm to carry accessory apparatus at any angle. Any thing that Mr. Tolles makes is sure to be made well.
The microscope is provided with a movable slide holder, serving as a substitute for a mechanical stage. This slide holder consists of a German-silver plate of very light weight, moving on a strong glass plate which forms the immovable stage; only four small points of the German-silver plate touch the top of this glass stage, while two prolongations of the former, bent downward and backward, and acting as springs, against the underside of the glass plate with just sufficient force to keep the slide holder in position, and to prevent it from slipping off when the instrument is inclined. Two small knobs facilitate the handling of this slide holder, and it is claimed that this arrangement exceeds in smoothness and evenness of motion the movable glass stages commonly used, while the movable part has less weight, and allows the glass plate to be of sufficient strength to guard against easy breaking.
The instrument has also plane and concave mirrors; sub-stage of the extra size required to receive standard sized English accessories; revolving diaphragms, etc. These are all attached to the swinging mirror bar, the axis of which is placed at the level of the object, so that The diaphragm and mirror swing concentrically around the object. The mirror can also be moved on the mirror bar to and from the object, and the distance between the latter and the sub-stage can be varied by reversing it. Both sub-stage and mirror can also be removed.
It is to be observed that in these two instruments the importance of the swinging bar, before described in connection with the Centennial and Histological stands of Mr. Zentmayer, has been recognized by Mr. Gundlach. The mechanism, however, by which these makers accomplish the swing in the plane of the object, is by no means the same in their respective stands. Thus the peculiar method of securing the stage to the limb, employed by Mr. Zentmayer, allows that the sub-stage with its accessories, and the mirror, be brought entirely above the stage, the only thing preventing a full revolution being the body tube, while. in the instruments of Mr. Gundlach the swinging-bar plays in a slot cut in the rear of the main stage plate, and the swinging motion is thus circumscribed by the stage slot.
This, although the least expensive instrument made by Mr. Gundlach, is nevertheless well put together, strong and really serviceable, and, with proper care, ought to last a lifetime. It can be readily made capable of doing most ot the work required by the physician and to those who can afford the luxury of having two stands something of this kind will be found a real convenience.
The sub-stage is fitted with the most complete movements for centering or for oblique light with the achromatic condenser. It has one-fourth inch movement each way; rack and pinion; divided circle for polarizing; is so arranged that the substage can be used either above or below the main stage and can be operated by hand or by tangent screws; lt is entirely separate from the mirror, but if desired can quickly be connected, so that the mirror and sub-stage turn together around the same centre, which is the thickness of an average slide over the stage.
The entire sub-stage with its milled heads can be taken off, so that there shall be nothing in the way when using direct light. The mirror is arranged so that it can be used in any direction, backward, forward, over or under the stage. The mirror and also the substage have graduated circles, so that the obliquity can be noted.
The movement of the body is effected by rack and pinion connected with two milled heads, which connect with the lever of the slow motion, thus preserving the distance between the objective and the eye-piece. The slide on the body tube is long and broad, thus preventing vibration or lateral motion when using the milled heads or the micrometer screw; the latter is grooved so that it can be used for photographic purposes.
The instrument is mounted on tripod base, with revolving platform. The platform is graduated, and upon it two standards are fixed, between which the instru ment turns to the angle when so used, or turning horizontally for drawing, or for measuring angular aperture. The center on which the instrument turns, when placed horizontally, is in a direct line with the object on the stage.
The binocular model is arranged with rack and pinion for different width of eyes; the prism is so fixed that the distance remains the same. The society screw at the end of the body is arranged as a safety nose-piece, with spring, so that the danger of breaking slides is avoided. The iris diaphragm has the society screw so that any objective can be used for a condenser, or it can be used above the objective as an adapter, to reduce the light in the instrument. The stand is nineteen inches high when arranged for use.
This stand and the “Centennial” of Mr. Zentmayer, may be considered as rival instruments, and neither of them enters the list for a slow race; both are respectively the masterpieces of their makers, and are claimed to be the very embodiment of all and singular that can be desired by the microscopist. Purely in the interest of the reader, we proceed to compare these stands with each other; the final verdict shall be left a matter of individual election.
First. The price of both instruments is precisely the same, while the Bulloch has additional the iris diaphragm, the mechanical stage with its adaptations for use as an object finder, the safety nose-piece, the duplex arrangement of sub—stage and mirror arm, whereby these move in unison, or independently of each other, and the centering and rotating sub-stage.
To meet this, it might be claimed, on the part of the Centennial, that the above—named additional contrivances have been purposely discarded by the maker of the Centennial; that really there is no particular advantages to be derived from the iris diaphragm, the mechanical stage, the centring sub—stage, or the duplex arrangement above referred to, and that all these contrivances serve unduly to complicate the instrument.
As to the centering sub—stage, it might be also said that with the introduction of the “ swing” there is no longer need of wide-angled achromatic condensers. Furthermore the secondary body of the Centennial being itself accurately centered, there is no occasion to introduce especial appliances for this purpose.
It will be noticed that in the Centennial the mirror and sub—stage rise without hindrance above the stage, the movement being only stopped by contact with the body tube (supposing the smaller stage to be employed,) all this time the mirror remaining in fixed focal position. To accomplish the rise of the mirror above the stage in Mr. Bulloch’s stand, the jointed arms connected with the mirror are brought into play, and indeed cannot be dispensed with. A close comparison of the mechanism will reveal the fact that in respect to the swinging arrangement,there is a wide difference in the construction of the two instruments. The angle of obliquity obtained with the Centennial stage, is greater than that obtainable in Mr. Bulloch’s stand.
The principal points are thus presented; it remains for the reader to use his own election. Either of the two stands will bear comparison with any foreign stand extant.
Mr. Bulloch also supplies another stand, which he calls his
The adjustable concentric stage can be centred to any objective; the edge of stage is bevelled and graduated, so that angles of crystals can be measured; it has a complete revolution. Its glass stage is perforated in the center, has brass fittings, so that the “Maltwood Finder” can be used; and its motion is perfectly smooth under the highest power. To the underside of stage is fitted a tube for accessories; this can be removed so that the utmost angle of oblique light can be obtained. Plane and concave mirrors and lateral motion for oblique light, coarse adjustment by rack and pinion, fine ditto, by delicate screw, diaphragm; draw tube graduated, with society screw at end. The instrument can be inclined to any angle, has English horseshoe base, and is sixteen inches high when arranged for use.
When the stage is not required to revolve, it can be clamped in any position by the milled screw shown in front; and when there is any danger of injuring the stage by the use of acids, the stage lifts out of the ring in which it revolves, and any ordinary piece of glass can be used on the ring by placing the instrument in an upright position. Rack and pinion quick motion, lever fine motion placed behind the limb moving the whole body tube; the body tube is fitted with broad guage screw one and a quarter inch diameter, and in which fits adapted with regular society screw, tripod base with single pillar, the axis on which the instrument turns is placed in such position that the instrument is perfectly balanced when placed in horizontal position for drawing. When so placed the centre of eye-piece is seven and a half inches from table, the standard is furnished with a B eye-piece. The mirror and sub stage can be fitted with divided arch for measuring the obliquity of light, the stage can also have divided circle for measuring the angle of crystals. Stand all made of polished brass.
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