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CIRCUIT STAGE VAN HEURCK MICROSCOPE:

c. 1910

Maker: W. WATSON & SONS LTD.

Serial number: 11970

DESCRIPTION HISTORY

Click on a picture to see more images and details.

 

DESCRIPTION

This compound microscope arises from an English tripod of the form used by Watson and similar to those used by Powell and Lealand and others. It is black with lacquered brass button toes which are cork shod. The limb is suspended by a trunnion joint with a rhodium or chrome-plated tightening handle. The spread of the toes is just slightly over 8 inches, despite the Watson catalog quoted spread of 7 . The distance from the bottom of the stand to the axis of rotation of the limb is about 5 1/8 inches. Across the rear of the tripod is a bar, a protrusion on top of which is where the limb makes contact when the microscope is in the horizontal position. The protruding piece also projects forward to make contact with the limb in the vertical position. Thus there are stops for the horizontal and vertical positions of the limb. It is signed on the bottom of the rear toe with the serial number, and at the upper end of the rear toe it is signed 'London'. The signature of 'W. Watson & Sons Ltd is engraved on the upward facing top curve of the 'Y'-shaped rear toe.

The gimbaled plane and concave mirrors are housed in a 2 inch lacquered brass casing with knurled rings to hold the mirrors in place. The mirror is supported by a black yoke attached to a a 1 inch long stem, which is in turn, attached to a tubular fitting which slides over the swinging tailpiece. The tailpiece swings on a brass screw attached to a downward protruding piece of the stage.

The substage support, separate from the mirror tailpiece, is fixed in position and also comes down from the stage. The substage has coarse focus by diagonal rack and spiral pinion. Fine substage focus is via a knob protruding upward from the stage. This knob, unlike the main fine focus knob, uncalibrated, but does have arrows showing the direction the substage is moved; clockwise moves the substage down, counterclockwise, up. There is a fixed ring for a condenser which has controls for centering the condenser. Unlike later models, the condenser housing does not swing out of the optical axis and so the condenser must be removed from the housing if it is desired to have the optical path below the stage without a condenser. A variety of condensers are with the instrument. These include a 'Macroilluminator' for very low power work, especially during photography, a 'Universal' Holos condenser, a 'Holoscopic Aplanatic Low Power Condenser', a 'Holoscopic Oil Immersion Condenser,' a 'Holoscopic Immersion Paraboloid, and a Substage Analyzer with Selenite cap with a nosepiece Analyzer. For more details of these, please see the accessories section below.

The Stage of this model protrudes further than in the No. 1 Van Heurck Model, and this allows full rotation of the 5 inch diameter mechanical stage with its protruding controls. The rotation is not calibrated, but the rotating edge is knurled. There is no easy provision for centering the stage rotation, which, like the calibration to the rotation was an extra. The mechanical stage has a one inch horizontal range, and a 1 1/16 inch vertical range. The optional calibration for these stage movements is a part of this instrument. These are calibrated 0-35 mm for the horizontal movement and 0-40 for the vertical, with a vernier to read tenths of a mm. The stage is controlled by two separate knurled knobs controlling horizontal motion by worm screw and vertical by double diagonal rack and spiral pinions. The optional stage bar with attached clips slides on grooves on the edge of the square part of the stage top plate. There is a knurled knob which can lock this bar in position. There is a hole near the bottom into which this locking knob can be screwed into. There are also two holes for the use of standard stage clips.

VH fineThe limb has a longer arm than the No. 1 Van Heurck to allow it to position the nosepiece in the center of the extended optical axis necessitated by the full rotation of the stage. Coarse focus is by diagonal rack and spiral pinion whilst the fine focus is via a long lever controlled from the top edge of the rear part of the arm. The knurled lacquered brass fine focus knob is calibrated and numbered from 0-10 with division increments of 0.1. It has arrows showing which directions of rotation lowers and which raises the optical tube. There is a steel pointer to register these calibrations. The instrument has a black triple nosepiece and it is signed with the Watson 'W' insignia. It is inscribed on its upper surface 'revolve' with a curved arrow pointing in the clockwise direction. Each of the three spots on the revolving nosepiece has a label for a lens, these being 2/3, 1/6, and 1/12. A variety of objectives are with the instrument and are described below with the other accessories.

The outermost main optical tube is of 1.5 inch outside diameter and is about 5 inches long. There are two calibrated drawtubes, the outermost and lower one being calibrated from 25 to 33 and also from 17 to 23 in one tenth increments with the whole numbers labeled. The inner drawtube is calibrated from 17 to 24 and is engraved similarly. The lower drawtube has a three inch range whereas the upper inner drawtube has a 3 inch range. The inner draw tube accepts a 31 mm diameter eyepiece, but there is also an adapter which allows the use of the narrower 23 mm eyepieces. A variety of eyepieces are with the instruments and are described in the accessory section of this web page.

All the rack and pinion fittings have the capacity for adjustment in the event of wear, as do the the slides in which the tubes and substage travel. Every part of this microscope works like it did over 110 years ago. The black finishes are a gloss black and the lacquered brass a mildly orange yellow. The black finishes of the stand probably have been professionally redone in some years past. The signatures on the foot, though readable, have no white coloring like most of the Watson stands from this era do. The white lettering of the triple nosepiece and the stage calibrations are intact.

case for CSVH scopeThe original case is heavy and large with a top handle as well as two side handles. It has dovetail joinery. There are two original accessory drawers, but no original draw inserts remain. The original magnification card has apparently been replaced with a typewritten magnification chart.

 



ACCESSORIES FOR THE c. 1910 CIRCUIT STAGE VAN HEURCK MICROSCOPE:

CSVH Microscope

Accessories for this microscope include two condensers, six objectives, polarizer with selenite cap, eyepiece analyzer, three eyepieces, a vertical illuminator, slides, compressor and livebox. There were also some Watson slides with it. The single condenser housing accepts both condensers.

Objectives currently with the instrument, all by Watson except as noted are:

VH obj
  • Achromatic 3 inch
  • Parachromatic 2 inch
  • Parachromatic 1 inch
  • Parachromatic 2/3 inch
  • Parachromatic 1/6 inch
  • Parachromatic 1/8 inch
  • Lietz 1/12oil immersion

Some readers may wonder how to compare these objectives to modern ones which are engraved as to magnification rather than focal length. A table listing the available Watson objectives, their focal lengths, n.a., and approximate magnification are provided on the Watson Objective Page. That page also relates some of this information to mechanical tube length. One should be aware that even now, as in the past, magnification is not only a function of the eyepiece and objective, but also the optics of ones own eyes; these differ from person to person so magnification will differ slightly between individual users of the same microscope. Put another way, even with a '10X' eyepiece and a '10X' objective, the true magnification will almost never be exactly 100X.

A variety of condensers and other stage and substage apparatus were available at the time this instrument was produced. The substage apparatus includes:

 

HOIC This later version of the 'Holoscopic Oil Immersion Condenser', is suitable for use with the highest power objectives and has an immersion front which may be removed for use with dry objectives of medium to high power. It is signed:  'HOLOS OIL IMM CONDENSER   5.5 mm     n.a. 1.30   WATSON   K5463'. This condenser housing fits the microscope but has no signature and requires adapters for the optical components; this condenser holder may not be by Watson.

 

 

Watson Polarizers and Analyzers In addition, there is also a polarizer to fit the substage with a selenite cap, along with a nosepiece analyzer, in addition to the a analyzer fitting over the eyepieces (shown above with the eyepieces). This set was also offered in the Watson Catalogs, as was the analyzer fitting over the eyepieces.

 

vert illumin vert illuminOther accessories include two vertical illuminators. One is the early brass type with a coverslip used as the reflector. The other is Watson's 'Combined Vertical Illuminator' set in a signed case, providing the option of a tiny prism or coverslip for reflecting the illuminating light beam. The Watson 'Combined Vertical Illumintor' was first offered by Watson after 1921, and is shown in the 1923 catalog (thanks to Dr Joe Zeligs for this information).
Vertical illuminators are used for illumination of solid or opaque objects with higher power objectives. Although with low power, top-illumination from the side can suffice, as the magnification increases and the focal length shortens, light cannot easily be directed onto the top of an opaque specimen. The vertical illuminators allow the light to come down onto the specimen from above through the objective, by reflecting incoming light off a coverslip at an angle (in the simpler model), or via a tiny prism or mirror which at the same time allows the reflected light to pass back up in the opposite direction reaching the eyepiece. With the coverslip type the reflected light goes up through the coverslip; with the tiny prism, it is so small, light is able to pass up the illuminator around it. These arrangements both have disadvantages and many years later, more inventive and efficient methods of illuminating opaque objects were developed. These included better vertical illuminators and also directing light downward around the outside edge of specially designed 'Epi' objectives. Examples of modern microscopes providing this type of lighting are in this collection including a Olympus Vanox with vertical illumination, and a Wild Epi-illumination system.

 

HISTORY OF THE EDINBURGH, VAN HEURCK, AND ROYAL MODEL MICROSCOPES

Henri Van HeurckThe famous Belgian microscopist, Henri Van Heurck(1839-1909) was the manager of his family business manufacturing paints and varnishes. He became famous as a botanist, expert microscopist, photomicrographer, and especially diatomist. More than one diatom species is named in his honor. The basic plan for the Van Heurck stand was based on the earlier Edinburgh stand, a model devised with the advice of an Edinburgh professor. For more historical information about the various models of the Edinburgh microscope see the Edinburgh B page and the Edinburgh H page.


edinburgh Watson & Sons had been making microscopes since about 1874. For some time in their early production, their microscopes were similar to other contemporary makers, but soon they started to produce a variety of interesting designs, including their own variation of the Walter Bulloch Biological No. 2, and also a version loosely based on Wale's New Working Microscope.   In 1887, Dr Edington, a Lecturer in Bacteriology from the University of Edinburgh suggested the first form of the Edinburgh stand; according to Watson's delivery records, the first example was sold on November 29, 1887. This stand was the inspiration for the Van Heurck stand, and like the Van Heurck, started out with a continental foot, but was soon ordered more often with a tripod foot. Like the Van Heurck, it was improved progressively over the years. This culminated in the Edinburgh 'D' and 'H' models, (an example of 'D' is shown to the left), which had most of the basic features of the (later) 'Royal' model. In fact, when the Royal was first introduced, it was actually slightly smaller than the Edinburgh H. The various Edinburgh stands were at first indicated by the numbers 1,2,3, and 4, but by 1890, the letters A,B,C and D were used. 


VHAIn  1889 or before, with all of his expertise, Van Heurck suggested the design of a microscope to his specifications, and this was the first model of the Van Heurck microscope made by W. Watson and Sons; the prototype was apparently delivered to Van Heurck in 1889*, but there is no entry in the Watson delivery book for the prototype. The first entry for a  Van Heurck in the Delivery Books was  March of 1891.  It was also pictured in the first edition of Van Heurck's book also dated 1891.  This first version is identical to the 'Watson No. 4 Van Heurck Stand A' seen in the 1893 catalog. Study of the illustrations shows that this initial Van Heurck differed from the original Edinburgh mainly in two features-the fine adjustment for the substage, and the ability to rotate the mechanical stage. Van Heurck preferred to do all of his photomicrography with a vertically oriented microscope which is why he preferred his microscope to be made with a continental 'horseshoe' foot and supported on a single pillar, so as not to interfere with substage adjustments during the, (then) delicate operation, of photomicrography with high power objectives. At the same time, many others preferred the horizontal position for photography. For this reason, his stand was also offered with the more stable English tripod foot which provided a much more stable stand for photography in the horizontal position. Many more examples with an English tripod exist than with the horseshoe foot, as the tripod quickly became more popular.

*An engraving of the Van Heurck 'A' stand was used as a frontispiece to the introduction in the Ninth Watson Catalog; the introduction in that catalog is dated 1889. I would like to thank Allan Wisner for supplying me with this information.


VHB As noted above, the Van Heurck instrument, as designed by the diatomist, was at first provided on a continental foot with a single pillar. Early examples had a standard one inch diameter main optical tube, as pictured in the image in the preceding paragraph. In the 1893 catalog the 'No. 4 Van Heurck Stand A' had a 1 inch diameter main optical tube with a single calibrated draw tube with tube length variable from about 160 mm to 260 mm. The 'No. 4 Van Heurck Stand B,' as shown to the left, had a double drawtube, the lower draw wider, (but still only 1.5 inches in diameter), and controlled by rack and pinion. In the 'B' stand the combined tube length could be varied from about 142 to 305 mm. It could be ordered as pictured with a continental foot, or for a slightly higher price with a tripod foot. The Van Heurck was apparently not yet considered the 'top of the line' instrument as No. 1 was the impressive 'Watson Swinging Substage Microscope,' No. 2 was the 'Scientist's,' and No 3. was the 'Research.'


VHB1896In 1896, stand 'A' was no longer listed, but the usual Van Heurck was still called the 'B.'   Also in 1896, the 'Grand Model Van Heurck Microscope Stand' was first listed in the catalog. At that time it was listed as identical to the B stand except for three new features: 1)concentric controls for the mechanical stage (after Terrell), 2)complete rotation of the stage, and 3)a slightly larger foot with the Grand, the spread of the foot 'more than ten inches'.

By 1898, the Edinburgh stand, which had been steadily improved, reached its final model in the 'H' but even the H continued to have small improvements added over the years.


VHCSThe 'Circuit Stage Van Heurck' was apparently first introduced about 1899 (as quoted in the Illustrated Annual of Microscopy for 1900). Like the Grand Model, it had complete rotation to the stage, but was otherwise identical to the smaller Van Heurck (now just called the Van Heurck without a letter or number), including the stage controls. Later on, the basic model simply became the 'No 1 Van Heurck'. Although listed in the Watson 1900 catalog, the Circuit Stage Van Heurck was not illustrated in that volume. The engraving to the left, from the 1902 catalog, illustrates the Circuit Stage Van Heurck with the optional Watson-Males two speed fine adjustment. It should be noted that from the start, the Terrell type stage could be ordered as an option for the Circuit Stage Model, thus some might look like a 'Grand' but would be distinguishable only by size.

To satisfy growing demand for a stand as perfect as the Van Heurck but slightly smaller and therefore less costly, the 'Royal' model was introduced about 1899-1900 as well. The major distinguishing feature between this and the No 1 Van Heurck, was the inability to rotate the mechanical stage (although some models with a rotating top plate are known); it was also of slightly smaller size than the Van Heurck, and initially was even slightly smaller than the Edinburgh H stand. In fact, it is a common misconception that the 'Royal' is generally a larger stand than the 'Edinburgh H' and this is not true. The tripod heights, arm/limb size, foot spread and stage are of identical size in many examples; what makes the 'Royal' appear larger is the larger diameter optical tube and drawtubes including the rack and pinion draw tube. Without these differences and the fact that some 'Royals' have a substage fine focus, the Edinburgh H and the 'Royal' could not be differentiated from one another. This is confirmed by the examples in my collection; the 'Royal' and Edinburgh are virtually identical in size and differ mainly in the diameter of main optical tube, the Royal's double draw tube, and fine focus for the substage.

The Van Heurck microscope was offered with many options, and some of these options were to leave off certain standard features for a discounted price. As noted above, it was eventually offered in three different models: the 'No. 1', the 'Circuit stage' and the 'Grand.' At any given time, the Grand was the largest. As noted above, the introduction of the Grand preceded the 'Circuit Stage' Model by about three years. These stands changed over the years and the 'Grand' Model from early years was more like the Circuit Stage model of later years, except for the size. Several features eventually distinguished the Van Heurk microscopes from the Edinburgh H and the 'Royal'. The first was a rotating mechanical stage (not to be confused with ability of the top plate of the stage to rotate, found on some other Watson stands as an option including some Edinburgh models), and the second was the double drawtubes, with the outer bottom one being adjustable by rack and pinion* .   Another feature found on these instruments (initially standard, later optional), was a fine focus for the substage, a feature found on relatively few microscopes at the time. Van Heurck himself preferred this to be controlled by a knob projecting vertically from the stage, as seen in the example at the top of this web page, but another option, quickly offered (and seen on the 'Royal' model in this collection), was to place the substage fine focus under the stage projecting horizontally, just above the coarse substage focus control. This below-the-stage version was apparently devised to satisfy some critics who complained that the vertical control interfered with stage access, but it was also slightly less expensive than the vertically projecting version.

Eventually many features and option of the Van Heurck were offered on the slightly smaller and less expensive Royal model. The one feature that was never offered on the ' 'Royal' ' was the rotating mechanical stage (although some models may have a rotating top plate, the entire stage does not rotate as a unit as in the Van Heurck models).  Although the 'Royal' was almost otherwise the equal of the Van Heurck, it should not be referred to as a ' 'Royal' Van Heurck' as Watson clearly distinguished it from all the Van Heurck models and never claimed it was a Van Heurk (see the discussion of this issue on the Royal Web Page.   In fact, Watson stated in their catalog that they produced the 'Royal' because of so many requests to modify the Edinburgh stand to include the features of the Van Heurck such as rack and pinion drawtube and fine focus to the substage. So in fact, the 'Royal' , like the Van Heurck was a derivative of the Edinburgh, but the 'Royal' started as an Edinburgh, not as a Van Heurck. It would, in fact be more appropriate to call it a ' Royal Edinburgh' as it is about the same size as the Edinburgh H, differing mainly in the diameter of the main optical tube and its double draw tubes. For a direct comparison of the Edinburgh H and the Royal, see the Royal and Edinburgh comparison Webpage on this site.

The Van Heurck was a work in progress and was continually improved and changed over the years. Early on, the main outer optical tube was as small in diameter as others but it was gradually enlarged to accommodate photography, initially one inch, then one and a half inches in diameter and later, this became two inches in diameter; this increase in tube diameter was also seen on the later versions of the 'Royal' microscope. The size of the foot changed many times over the years as well. The condenser housing on the model shown on this page could not be swung out of the optical axis, but that feature was added later, not only to the Van Heurk models but also to the 'Royal' and the Edinburgh too. Initially the mirror was on a swinging support, but this was abandoned in later models.

As more improvements were made, many were offered as options. It is a common misconception that the 'Grand' Model had more features by nature, but in reality, as time went on, all the Van Heurk microscopes had almost all the same optional features, except as noted below. These option included calibrated verniers for the stage X and Y motions (found on the example here), graduated rotation to the stage, rack and pinion stage rotation, adjustable centering of the stage, locking for the stage position, and rotation to the substage.  A two speed Males-Watson fine focus was eventually an option on the Van Heurck with separate adjustment wheels for each speed; this option could be ordered on most other Watson microscopes at that time; see the Holos Fram, for example.   Another option was the location of the substage fine focus as noted above; eventually the very presence of the substage fine focus was an option.

The main permanent differences between the three models of Van Heurcks were the ability to fully rotate the stage on the Circuit stage and Grand Models (but not on the the No. 1 where the stage could rotate, but not 360 degrees), the concentric mechanical stage controls for the Grand (but also available as an option for the Circuit Stage Model, starting in 1900), and the size of each stand, the Grand being the largest, the No 1. and the Circuit stage being smaller.   Because of all the possible combinations of options, and also because their size changed over the years, few Van Heurck Models are exactly alike. A chronology of these developments follows, and a comparison of some of the features of these microscopes is noted in the table below.

CHRONOLOGY OF EVENTS IN THE DEVELOPMENT OF THE EDINBURGH, ROYAL, AND VAN HEURCK SERIES OF MICROSCOPES:

  • 1874-: Watson starts to produce microscopes.
  • 1874-1887: Watson produces microscopes of the usual designs but eventually makes their own version of other famous stands including those of the American makers, Bulloch and Wale.
  • 1887: The first Edinburgh microscope is sold, based on suggestions by Dr. Edington of Edinburgh.
  • 1889: Henri Van Heurck proposes the initial design for his microscope.  
  • 1889: The first Van Heurck microscope, apparently a prototype is pictured as the frontispiece of the Watson 1889 catalog, but not listed.   The engraving is identical to the engraving in the 1893 catalog for the Van Heurck 'A' Stand.
  • 1891: The first entry in the Watson Delivery Books of a Van Heurck microscope, being based on the Edinburgh stand. It had a 'horseshoe' foot.
  • 1893: The Watson Catalog offered the No. 4 Van Heurck microscope in two versions both with a horseshoe foot; Stand 'A' had only a single drawtube and did not have a rack and pinion adjustment to the drawtube. Stand B had a larger diameter main optical tube with two drawtubes, the lower one adjustable by rack and pinion. Either version could be obtained with a tripod foot as an option for additional cost.
  • 1895: The 'Grand Van Heurck' is first offered, and is seen in the 1896 catalog with the new features being complete rotation to the stage, the concentric controls for the mechanical stage, and the slightly larger size of the stand. The Van Heurck 'B' is offered but the 'A' with single drawtube is no longer mentioned. The grand is 7/8 inch taller than the 'B.'
  • 1900: The 'Circuit Stage' Van Heurck Model is introduced. It has the complete rotation of the stage but is otherwise identical to the 'B' stand.
  • 1900: The 'Royal' is also introduced,  smaller than the Van Heurck models, but with options for almost all the same features except for stage rotation; the 'Royal' was never offered with stage rotation.  It is initially slightly smaller than the Edinburgh 'H' model!   Standard features included the double drawtube with rack and pinion adjustment to the lower one.  Initially, substage fine adjustment was standard on the 'Royal' but located under the stage near the substage coarse adjustment.  Later this became optional.  

*-It becomes even more confusing, because eventually, even the rack and pinion adjustment for the drawtube could be ordered as an option on 'lower class' microscopes such as the Edinburgh stand.

 

OPTIONS FOR THE MICROSCOPES:
The following table lists options (including optional deletions) for the Edinburgh, Royal and Van Heurck Models. It may be incomplete, as the author has not had access to every single Watson catalog relevent to the period.

VAN HEURCK NO. 4, 'A' MODEL
DATES STANDARD
FEATURES
OPTIONAL
FEATURES
1893 Horseshoe foot, single draw,
Mechanical Stage with separate controls for horizontal and vertical motion which rotates but not a full 360 degrees,  Substage Fine Adjustment, Projecting upwards in back of stage, clamping lever for inclination Joint.  The mechanical draw-tube length can  vary from 160 to 260 mm. 
Tripod foot, Binocular Body,  Centering Screws to stage with clamping, Rackwork rotation to stage, Divisions to stage, Divisions to Horizontal and Vertical movements of stage, Rackwork rotation to sub-stage,  Clamping of substage centering,
1896 The 'A' Stand is no longer offered in the catalog
VAN HEURCK NO. 4, 'B' MODEL
DATES STANDARD
FEATURES
OPTIONAL
FEATURES
1893 Double Draw, with one Mechanical Draw tube, otherwise same as 'A'  but with the extra draw-tube , the mechanical tube length has a longer range of from 142 to 310 mm. Tripod Foot, Binocular Body
1896 Tripod Foot now standard, otherwise same as 1893 same as 1893, except now the Horseshoe foot was optional
VAN HEURCK NO. 1
DATES STANDARD
FEATURES
OPTIONAL
FEATURES
1900 Same as Van Heurck B of 1896 Same as 1896  with additional option of Strnger's fine adjustment
1902 same Same but also the Males-Watson fine adjustment and the Spindle head fine adjustment AND hinged substage which can be turned aside out of the optical axis
1906 same same
1912 same except now the substage fine adjustment is an option Choice of above or below stage substage fine adjustment
1918 same except now all Van Heurcks have hinged substage standard, which allows the substage to be turned aside  and out of the optical axis same as 1912
1921 same as 1912, but now the substage bar extension sliding on dovetail to allow greater range of accessories of different heights as was previously only offered for the Grand, then the Circuit stage, is now offered for all VanHeurcks 
1923
VAN HEURCK CIRCUIT STAGE MODEL
DATES STANDARD
FEATURES
OPTIONAL
FEATURES
1900 Identical to No. 1 but with complete stage rotation Identical to No. 1
1906 Same as 1900 Same as 1900
1912 same except now the substage fine adjustment is an option Choice of above or below stage control of substage fine adjustment
1918 same except now all Van Heurcks have hinged substage standard, which allows the substage to be turned aside  and out of the optical axis same as 1912, but now the substage bar extension sliding on dovetail to allow greater range of accessories of different heights as was previously only offered for the Grand 
1921 same as 1918 same as 1918
1923 ---- ----
VAN HEURCK GRAND MODEL
DATES STANDARD
FEATURES
OPTIONAL
FEATURES
1896 Identical to the Van Heurck 'B' Stand, with the addition of concentric controls for the mechanical stage, and extension of the stage and arm forward to allow complete stage rotation and larger overall size. Identical to Van Heurck 'B' model.
1900 Identical to Circuit stage Model, but larger Identical to Circuit stage model but optionally the same stage as the No. 1 instead of fully rotating, reduced the price by 3 pounds. 
1902 Identical to Circuit stage Model, but larger Identical to Circuit stage model but optionally the same stage as the No. 1 instead of concentric controls, reduced the price by 3 pounds.   Also option of Stringer's fine adjustment, or Males-Watson Two speed fine adjustment, or Spindle Milled-head fine adjustment, all at extra cost.
Optional hinged  substage so it can be swung out of the optical axis.  
Also a substage bar extension sliding on dovetail to allow greater range of accessories of different heights.
1906 Identical to 1902 Same as 1902 but also offered the Scop Mechanical Stage instead of the usual circuit stage, price the same as the standard model.
1912 same same as 1906
1918 same except now all Van Heurcks have hinged substage standard, which allows the substage to be turned aside  and out of the optical axis
1921 Same Side Limb or Horizonatal fine adjustment for same price.

The author would like to thank Dr Joe Zeligs and Allan Wisner for help, references and advice on this page.