DESCRIPTION: This is a fine example of a monocular Ross Bar Limb microscope, made by the originator himself, Andrew Ross about 1847. It arises from a 'splayed' Y-shaped foot on two thick flat uprights, each with an attached buttress at right angles to add stability. It is signed on the foot: 'A. Ross, London. No.324' The limb, essentially a large box into which the 'bar' slides for coarse focusing by rack and pinion, is supported upon the uprights by trunnions. Protruding down from the bottom of the limb is a round tailpiece onto which the large (3 ¼ inches outside diameter) plane and concave mirror fits. The mirror is gimbaled and can slide up or down the tailpiece on a ring and can revolve fully on the tailpiece. The fine focus is the standard Ross long lever fine focus through the arm; the lever can be seen inside the arm when viewed from underneath it. The arm can rotate clockwise 90 degrees (rightward, as seen from the rear), for full access to the stage; there are stops at the normal and 90 degree positions. This feature of stops at the normal working position, and 90 degrees clockwise, are mentioned in Carpenter's first edition of The Microscope and its Revelations of 1856. These stops were not present in the earlier versions of Ross' Bar limb like No 161 also found on this site. The arm does not rotate to the left.

The bar on this microscope, as in all the earliest Ross Bar limbs, is nearly triangular in profile; the front apex of the the 'triangle' is flattened, creating what is technically an isosceles trapezoid with a very short base on that side. It is quite thick (about 1 ⅛ inches thick), compared to the smaller triangular bar in later second class microscopes made by Ross. The bar registers its four sides against the pinion box but not at the corners, as those areas where the corners of the bar would meet the pinion box are enlarged slightly to prevent the corners from being in contact with the pinion box.

There is a mechanical stage controlled in the X and Y axes by knurled knobs. The square top plate of the stage can be manually rotated, and can slide back and forth. It has a fixed ledge at its rear and the slide is held between that fixed ledge and a bar that slides back and forth on the top plate. The sliding bar has a spring loaded pressure fitting at its center to grip the slide. The top stage plate has a hole on the right and also on the left to accept the stage fitting accessories such as the stage forceps, frog plate, etc.

The substage has focusing by rack and pinion. Before the dedicated substage was popularized, most makers attached substage accessories to the underside of the stage. In the case of Ross Bar Limbs, and also Smith microscopes, this was accomplished by a dovetail under the stage and before that by fingers on Ross Bar limbs. This substage dovetail facility is present on this microscope, perhaps suggesting the rack and pinion substage was a slightly later addition. The microscope comes in a hardwood case with a supplementary accessory case. The microscope and accessory box as well as the bench condenser, etc all fit the box well, but the height of the microscope is short for this case and so it may not have been original, though likely from the same era. The microscope fits into a sliding platform inside the bottom of the case. The main case has furniture to hold the frog plate, and the bench condenser and likely had other fittings that have been lost over the years. The accessory case fits inside the main case, and contains its full complement of accessories, some of which may not have been available at the time this microscope was made. Therefore, like many other Ross microscopes now known, at least some of the acccesories, and even the case, may be later additions. Two of the objectives are signed with dates in the 1850's, supporting the idea that this microscope was updated during that decade.

ACCESSORIES INCLUDE:

1. Five objectives
2. An adapter for the 1 ½ inch objective to allow it to fit on to the nosepiece
3. Four eyepieces
4. A Ross-type silver side reflector
5. Stage bullseye condenser
6. Two different size liveboxes
7. Removeable centering apparatus for the substage
8. A stacked rotating selenite fitting with three rotating selenites
9. A large polarizer fitting into the bottom of the selenite fitting
10. A wheel of apertures that slides into the dovetail under stage
11. Three sleeves that screw into the substage ring which is itself controlled by rack and pinion
12. An Achromatic condenser that threads into the centering apparatus
13. Two dark ground condensers that also fit the centering apparatus
14. A very large diameter dark ground condenser fitting into the larger diameter sleeve
15. A Wenham-type Paraboloid dark field condenser
16. A large frog plate(51.5 X 152 mm with a 33 mm glass window)
17. A large freestanding bench Condenser
18. Lieberkuhn fitting over the ½ inch objective

HISTORY OF THE ROSS BAR LIMB MICROSCOPES:
Two famous firms reported Bar Limb microscopes in 1843, namely Hugh Powell and Andrew Ross. Some would give Ross priority due to the fact he said he claimed he had made many before that date, but Powell's description was published one month earlier in the year, thus leading some to credit him.

In any case, Andrew Ross, the more prolific of the two, first constructed microscopes for the trade, and his initial microscopes are likely signed by others. The first microscope clearly known to be of his make was the simple and compound microscope he made for Valentine in 1831 and it was reported in the Transactions of the Society of Arts of 1832. Ross went on to make his Lister Limb microscopes of various designs until 1843 when he first came up with his famous microscope with a Bar Limb and Splayed foot, supporting the limb between two uprights. This design, along with its accessories, was first reported in the London Physiological Journal of 1843, and continued to be Ross' standard design until his death in 1859. Following that, the design was continued by his son Thomas, who added improvements, such as the Wenham Binocular tube (1860), as they became available. The signature on the microscope on this page is that used by Andrew Ross between the years 1847 and 1859. Serial numbers from that period range between about No. 230 and No. 1857 or higher. Therefore, one can conclude that serial number 324 is from about 1847.

As noted above, the accessory case is likely a later addition, and contains some apparatus that is actually dated later, and other things, such as the stacked selenite fitting for the substage, that apparently were not available, or at least not listed in the Ross catalogs, at the time this microscope was originally made.

SUBSTAGE ARRANGEMENT:
A word about the substage arrangements of the Ross Bar Limbs is in order. As can be seen in the images to the left, starting with an image of the Ross Bar Limb No 323, at first the substage apparatus attached via a sliding dovetail on the bottom of the stage, but sometime, perhaps in the 1840's Ross started to supply rack and pinion substages. As seen in the next two images, of Ross No 324, the microscope featured on this page, the rack and pinion was added despite the persistance of the dovetail fitting under the stage. There is an advantage though to leaving the dovetail there and that is the ability to use the wheel of stops that slides into it to regulate the size of the cone of light passing through the specimen when the mirror is used without a condenser. Later on, this feature, a ring of apertures to regulate the diameter of the illuminating light source, was built-in to some condensers. This is needed to create optimal illumination, because the top element of the condenser needs to be close to the slide and the aperture in this case must be built in to the condenser below some of the optical elements*. Since the dovetail arrangement remains on the vast majority of Ross microscopes until the rack and pinion substage became more common, perhaps in the late 1840's, it may be that the rack and pinion arrangement here was part of a later upgrade just like the some of the accessories, which are likely also later. Judging from the image of Ross No 323, it would appear that it would be quite straightforward to add the rack and pinion to the substage as originally configured. Rack and pinion substages are found in most(but not all) examples of Ross' first class bar limb microscopes dating from about 1850.

*Later on, it was also discovered that adjusting the lightsource so that it was imaged in focus on the condenser aperture provided optimal illumination improving resolution. This became part of the illumination technique known as Kohler illumination.

This microscope sold for $3660 (in 2019 dollars) in 1985 at a Phillips auction. It was in its current configuration and had the current accessory case with it at the time.

The author is very grateful to Dr Joseph Zeligs for his careful proofreading of this page, and helpful suggestions and for supplying catalog information as well as additional reference materials.