DESCRIPTION:

This an early example of a monocular compound bar-limb microscope made by Andrew Ross. It has a Y-shaped foot which is cork shod on the bottom 3 contact points. The foot is signed AndW Ross, London, N^o. 161 (This signature dates the microscope to after 1841, but before 1847; (see history below). Flat uprights with inward buttresses arise from the foot to support the microscope. These uprights are attached by joints on each side of the pinion box/limb housing box. The tension on these joints can be adjusted by the screws, and with the correct amount of tension, the microscope will be securely positioned to any angle of inclination from vertical to horizontal. The stage has about a one inch travel in both the X and Y directions controlled by the two horizontal knobs under the right-hand side of the stage. The top plate of the stage has a hole on the right and on the left to accept stage-mounted forceps or other accessories. The coarse focus is by straight rack and pinion acting on the apex of the trapezoidal bar which has a rack machined into it. The top half of the bar has a isosceles trapezoid shape in cross section; a long section at the bottom of the bar has been machined to a round shape, projecting through a hole at the bottom of the gear box/limb housing, and can be seen to move up and down as the limb is focused by the coarse focusing knob. The tension on the trapezoidal portion of this bar can be adjusted by three screws on the front of the pinion box/limb housing(right). The larger screw in the middle acts on a heavy brass leaf spring inside which presses against the wide flat surface of the bar. The other two screws adjust the tension of two contact points at the top of the pinion box. These screws allow adjustment for wear and when properly adjusted, just the right amount of tension on the bar to prevent it from falling under the weight of the arm and tube is easily achieved. Fine focus is controlled by a knurled knob on top of the limb acting on a long lever. One revolution of this knob moves the objective 1/500th of an inch. The nosepiece is sprung thus reducing the chance of damaging the the glass or object under observation. Another taller knob holds the arm in place, tension inside imparted by a coiled spring. When loosened, the arm may be rotated away from the stage in either direction. The arm may be completely removed if desired; in the 1840s, another arm for single lenses could be substituted.

MECHANICAL STAGE AND SUBSTAGE APERTURE DISK:
The mechanical stage is supported on an L-shaped bracket screwed onto the front of the pinion box/limb housing. The tailpiece holding the gimbaled mirror is screwed in to the bracket. The mirror support is screwed into the tailpiece at a fixed distance from the stage. The controls for the mechanical stage project below the stage and are situated next to each other, as seen from the front of the microscope. The knob further away from the stage acts on a rod which has a rack cut into it and controls movement in the X-axis. The pinion of the knob closer to the stage acts on a rack cut into the bottom plate of the stage to move the stage in the Y-axis.
The bottom of the stage is blackened to avoid stray reflections of light. Accessories slide into the underside of the stage to fit into brackets at its rear.

A disk of apertures on a rectangular plate fits in this location (see accessories, below).

ACCESSORIES:

This microscope came to me with a single low power objective with the initials R D engraved in script on it. I added a 1/4 inch Ross objective from 1852. There are three Ross eyepieces. A Ross camera lucida can replace the cap on the eyepiece. Two original live boxes, referred to in the literature of the time as Varley's Animalcula Cages are also present. Varley's improvement was the black trough around the central disc that serves as a resevoir for the fluid medium that the specimen would be in, reducing the speed at which it would dry out. Another accessory is a silvered stage-mounted side reflector for illuminating opaque objects from above. A rectangular plate with a disk of apertures, slides in along the bottom surface of the stage, held on by two fingers at the back of the stage bottom; this plate, like other substage accessories, has a screw in front to register in a a short round hole at the front of the stage, allowing adjustment for centering in the Y axis as well as providing a third point to hold the plate securely in place. The aperture wheel has four little brass knobs projecting down to rotate it into any of its four positions, each registered by a click-stop. There are three different size openings and one position that has no opening. Additional substage accessories, each on their own rectangular plate would slide into the same position. One of these for example, a condenser with integrated rack and pinion focusing; a fairly accurate facsimile of the latter is also with the microscope, the plate being fabricated anew, and the focusing portion sourced from a group of spare parts and gifted to Barry from Jurriaan. It uses a short objective as a condenser, a 2/3 inch by Swift currently in place. Although the pin in front of the plate provides centering in the Y axis for substage accessories, centering in the X axis is provided by slightly rotating the arm supporting the main tube right or left. Since this movement is in an arc, it may require a slight adjustment in the Y axis after the movement. A stage forceps is also present. As seen in the illustration from 1843 to the left, other accessories could include additional eyepieces, a stage-mounted bullseye condenser, frog plate, a lister-type compressor, and a supplementary arm for use with simple objectives for e.g. dissection. Obviously, additional objectives were also available.

HISTORY:

Andrew Ross (1798-1859) published a paper for a simple microscope in 1832. He is known to have signed his instruments from about 1831. Before, and possibly also while signing his own instruments, he was a maker for the trade. He quickly became the foremost maker of microscopes in England, producing instruments of good quality. Among the earliest known Ross microscopes, dating to about 1831-2, are a simple and compound microscope for dissection designed by the botanist William Valentine. This microscope was not inclinable and was focused via a knob under the foot, a feature previously found in some of the microscopes of the 1700s. Its description was published in 1832 in the Transactions of the Society of Arts, Manufactures,Commerce &c., Vol XLVIII and is shown here to the left. Ross is well known for his invention of the correction collar for objectives, an early example of which is in this collection.

His next microscopes were variations on the Jones Most Improved plan. But instead of a simple inclination joint, these microscopes featured a ball-and-socket inclination joint and were made until the mid 1830s. They usually featured a flat tripod foot, but a microscope of this type with a round foot, likely made by Ross, but signed by Cary is in this collection.

In the mid-1830s, Ross started to produce Lister limb microscopes and this continued until the early 1840s. An example from about 1836-7 is shown on this site, and to the left. Coarse focusing was by a rack and pinion, the rack attached to the inner tube and the pinion attached to a knob on the outer tube. This same arrangement was used later by others such as Powell & Lealand who used it on their Iron Microscope

Ross authored an article for the Penny Cyclopaedia in 1839. In the Penny Cyclopaedia he pictured a simple dissecting microscope (left), and a Lister Limb compound microscope (right). Note that the rack for coarse focusing was now machined onto the limb.

Ross' first form of bar-limb microscope with a splayed Y-shaped foot with flat uprights was first illustrated in the London Physiological Journal of 1843. This instrument is identical to the one featured on this web page with the exception of the design of the mechanical stage, and in some examples, a steadying support from the arm to the tube. The initial form had the knobs for the X and Y stage motions oriented 90 degrees to each other and at the level of the stage. The movement in the X-axis was via a rack machined onto a bar that was part of the fitting which supported the top plate, similar but not identical to the model featured on this page above. The Y-axis movement was controlled by a pinion acting on two racks on the plate underneath the top plate. This form of stage was made for only a very short time, few examples remain extant.

As featured on this page above, the next form of Ross bar-limb was, identical to the first but included a different stage. This stage, with controls next to each other, and located under the stage is easier to use than the previous model where the controls are oriented 90 degrees from each other. This model was also made for only a short time, all known examples being datable to 1843 to 1845.

It was in 1845 that the stage changed again to have both controls located next to each other but now projecting horizontally, a position they remained in for many years thereafter. A few Ross microscopes were also equipped with Turrell stages, and at least some of these stages were made by Powell & Lealand and adapted to the Ross microscopes. It was also about 1845 that a rack and pinion substage was added. In the early versions with this type of microscope, there was also the facility to slide an accessory on to the bottom of the stage, but instead of this plate being supported by two fingers at the back as in the earlier model, it slid into a dovetail incorporated into the bottom of the stage. The rack and pinion substage screwed on to the bracket as seen in the example numbered 324 on this website. This microscope is shown to the left.

It is also notable that the bar orientation was changed such that the apex of the isosceles trapezoid was then oriented towards the front of the microscope while the wide base was oriented to the rear and now had a rack screwed on to the wider flat surface instead of being machined directly onto the narrow apex of the trapezoidal bar.

Sometime between numbers 161 and number 324, a rack and pinion substage was introduced. Attaching the rack and pinion mounting for substage apparatus to the substage bracket prevented the attachment of the tailpiece for the mirror to the bracket, so, as shown to the left, the tailpiece supporting the mirror was moved back and, as shown to the right, attached to the bottom of the pinion box/limb housing instead (mirror removed for clarity). The rod at the bottom of the bar limb then slid unseen, inside the tailpiece, enlarged in diameter to accomodate it. Another change was the the mirror support was a ring that could be adjusted to any position up or down the tailpiece, and the ring could rotate around the tailpiece partly or completely out of the optical axis.

The No 1 Ross microscope stage eventually was made round with graduated rotation by a pinion projecting underneath the stage as shown on the Ross exhibition microscope on this site.

CONDITION:

When received this microscope was in very poor condition, having been neglected and stored in an attic for many years. It was heavily tarnished with areas of verdigris, and had both missing and broken screws. The entire instrument was completely disassembled, cleaned, and refinished, respecting as much as possible its original appearance and preserving the engraving and machining marks. It now appears and functions essentially as it did originally. This project took about 70 hours to complete, not including the time required to prepare the lacquer.