ROSS MICROSCOPE

DESCRIPTION: Signed in block Capital letters on the Foot: 'ROSS'. In addition, signed in old English on the next line 'London.' and then the serial number '3727.' on the third line. It is also signed on the optical tube: Wenham's Binocular by Ross London.

The massive rectangular bar-limb is supported between two trunions arising from the foot and each supported by braces facing 90 degrees inward. The inclination joint has a lever tension adjustment to maintain the inclination chosen. A large knob fastens the bar to the arm. Coarse focusing is by rack and pinion, fine is by a graduated knob to a long-lever screw.

There is a graduated mechanical stage which can rotate manually, or by rack and pinion control from the underside of the stage; the pinion can be pulled down to disengage it and thereby allow manual rotation.

The substage can be moved up or down via rack and pinion motion. The substage has fine centering controls and it too is graduated, and can rotate via rack and pinion adjustment, similar to the stage above.

The large mirror has a plane side and a convex side and has a triple articulation leading to the gimble. The mirror support can slide up or down the tailpiece.There are a large number of adjustment screws.

This is the largest microscope ever made by the Ross company and is second in complexity only to the Wenham Ross Radial. It is also the one of the two largest brass microscopes in this collection, possibly the largest ever made commercially. Other than modern microscopes, in this collection only the Bulloch Congress model is heavier. This Ross came in a glass-fronted case with a separate mahogany case for an extensive set of accessories, many of which are still present.

Accessories include:

1. Three pairs of eyepieces labelled A,B, and C, and a single D signed 'Kellner's orthoscopic Ross London.'
2. Wenham-type parabolic darkfield condenser
3. Low power darkfield condenser
4. Nosepiece analyzer
5. substage Polarizer with wheel of apertures
6. Achromatic substage condenser signed 'Ross London' with double wheel of apertures
7. two different size combination compressor-liveboxes
8. stage forceps
9. two signed Lieberkuhn reflectors
10. a Beck vertical illuminator
11. a dark-well holder fitting into the substante with 3 darkwells
12. a double nosepiece
13. Six objectives
14. substage ground glass fitting
15. substage blue glass filter
16. a large fish plate
17. a monocular tube extension

HISTORY OF ROSS BAR-LIMB MICROSCOPES

Andrew Ross founded his business in 1830, and like James Smith, collaborated with J.J. Lister, the man who invented a mathematical method of producing objectives which were both achromatic and aplanatic. Ross's early instruments were constructed initially in a fashion similar to the Jones-most-improved models, followed by a construction similar to that of the 'Lister Limb' and he continued this practice until the 1840's when he developed his version of the Bar-Limb, a very stable design and from then on also supported his larger stands on the classic Y-shaped foot with two upright supports. Ross Bar-limb construction was first pictured in the Physiological Journal of 1843. Early examples used a triangular bar, which was later replaced by a square one and finally on the largest and heaviest version, a rectangular one like seen here. Andrew died in 1859 and his son Thomas Ross carried on the business, and displayed a microscope similar to this one, (except for being monocular) in the 1861 Great Exhibition. Thomas Ross died about 1870. Francis Wenham, for some time a consultant working for Ross, invented one of the first long-lived designs for a binocular microscope about 1860-1861. Wenham's binocular was incorporporated into the instrument seen here. It was Professor J.L. Riddell of New Orleans who invented the first binocular system which was practical other than at the lowest magnification; although Riddell's invention was in the middle of the 19th century (1854), it seems it was slow to be adapted. The Ross company went on to produce optical products well into the twentieth century, although large high-quality microscopes became less important as the years went by. The engraving below (taken from the 1883 edition of Carpenter's 'The Microscope and Its Revelations'), shows a microscope virtually identical to the present one shown here, except for the sliding arc fitting for locking the stand, the one seen here having the tension-adjusting lever acting directly on the inclination joint. By 1883, Ross' catalog of microscopes shows only the Lister limb Ross-Zentmeyer stands and this model, although presumably available by special order, was no longer part of the standard offerings. As Carpenter said:

'Its disadvantages consist in the want of portability...and liability to tremor in the image when the highest powers are used, through the want of support to the body tube along its length'...and this has 'induced Messrs. Ross to adopt the Jackson-model...'

The Jackson model is essentially a Lister Limb. Thus the 1883 Ross Microscope catalog featured the Lister-Limb based Ross-Zentmeyer construction. Powell and Lealand did not follow suit however and continued to use Bar-Limb construction into the twentieth century, although in some examples they used a support from the top of the optical tube to the back of the arm to form a more rigid support to the tube.