HISTORY OF THE POWELL & LEALAND No 1 MODEL MICROSCOPE STAND

Although larger model microscope stands had been produced by Hugh Powell, notably the massive stand commissioned by the Royal Microscopical Society in 1840, what is now known as the No 1 Model was a direct development of Powell & Lealand s new tripod-based stand of 1843, seen to the left, click on the image for larger and additional images. As shown here, this stand was first described in that year s November issue of The London Physiological Journal as Powell & Lealand s new microscope . This is supported by a lighter version of the tripod, which carries the body on trunnions, and a transverse arm, which contains the long lever, which moves the nose piece fine-focus adjustment. Initially, the fine-focus screw, which operated a cone, was placed on the right side of the arm. In 1847 this was moved to the familiar vertical position on the top of the arm, immediately behind its pivot. At this stage, the microscope tube was also supported by a set of diagonal stabilizing struts extending from the back of the arm to the upper third of the tube. Sometime during the early 1860's these were abandoned.

Powell & Lealand did not enter the 1851 Great Exhibition, but it is believed that during this time they worked on a larger model based on this design. Dated examples are extant from this period, with the more solid rectangular feet as in the later No 2 stand, either with or without the supporting struts. These could be regarded as the 'proto-No 1/No 2 stands', from which the later models were developed. Two examples of these, called the Improved Large First Class Microscope are found on this site, and still have struts supporting the tube. The more detailed account of the Improved Large First Class model, dated 1854, includes many additional details about it and its history. As seen in the image to the left, the Improved First Class stand of 1856, is similar to the 1843, stand other than the position of the fine focus knob, the rack and pinion substage, the design of a heftier tripod, and the rectangular and heavier tripod legs.

The next model(left) was worked on at odd times, and appeared in 1861. It was similar in outline and appearance to the final No 1 design, save for the massive ring attached to the limb, within which there was a second ring carrying the stage to which the substage was attached, allowing both to be rotated by the same rack-and-pinion movement, with separate rotation also provided for the substage. An example of this model was ordered by the Radcliffe Library for use by The University Museum, Oxford, in 1864, together with a 1/50-inch objective amongst the accessories. This model continued to be made until the definitive version of the No 1 model stand was put on the market in 1869. The main modifications involved the construction of the rotating stage, which this time was mounted in the same plane as the ring, and there was a separate carrier for the centering and rotating substage, attached below the stage now, and not rotating with it as in the previous model. In this form, the Powell & Lealand No 1 microscope continued to be made unchanged for another 40 years, until the firm quietly faded out of existence during the first decade of the 20th Century. The only additions were a fine adjustment to the substage (1882), rack work to the monocular draw tube (1887), and diagonal rack work to the coarse adjustment, all at the suggestion of E.M. Nelson, an eminent microscopist, and user of this model. After the appearance of Zeiss apochromatic objectives in the late 1880s, an exchangeable shorter continental drawtube of 160 mm was also made available, this being one of the few microscopes at the time with a fine adjustment precise enough to take full advantage of these. Not long after this, Powell & Lealand developed their own apochromatic objectives for the longer 250 mm English tube.

The Reverend Dr. William Henry Dallinger, F.R.S. (1839-1909), parson-naturalist and microscopist, was an enthusiastic user of the Powell & Lealand No 1 microscope, and the 1891 and 1901 editions of Carpenter s The Microscope and its Revelations, edited by him, include four engraved plates depicting the No 1 stand in use for different methods of observation. The painting of Dallinger in the Wellcome collection by Edgar Herbert Thomas, shown to the left, depicts him in academic gown seated at a binocular Powell & Lealand No 1 microscope. Note the similarity to the microscope pictured and discussed on this page. Dallinger also used a special stand, allowing the microscope to be used vertically for fluid mounts(right). He conducted research into saprophytic organisms, and with the extensive signs of use on the fine adjustment, and on one of the live boxes, it is tempting to speculate that he may have been the original owner of this very microscope, particularly considering the striking resemblance to the stand here discussed. Dallinger, being an author of books about the microscope, would be a good candidate to want to have all the various P & L objectives to write about in his book. Definitive proof to support this hypothesis is lacking, however.

HISTORY OF THE POWELL & LEALAND FIRM

Hugh Powell(left) was born in 1799, and in his early working life he was a philosophical instrument maker to the trade, which in those days meant that one s work was often signed and sold by other retailers. The first mention of him is in 1831, regarding the first of three simple dissection microscopes made by him for Cornelius Varley (1781-1873). They both lived in the same neighborhood of London, Somers town. Varley was an inventor himself, and patented his graphic telescope in 1811. He was also a microscopist, and a painter, his favourite medium being watercolours. He was also one of the 17 gentlemen who met at the house of Edwin Quekett in 1839, to form the Microscopical Society of London, later the Royal Microscopical Society. It is also known that Powell was making mechanical microscope stages designed by the engraver, Edmund Turrell, who also produced some of Varley s illustrations for The Transactions of The Society of Arts, so there were many interconnections between men involved in microscopy.

Varley s nephew was Andrew Pritchard (1804-1882), and for some time Hugh Powell made a number of microscopes for him, whilst other examples of this Pritchard design were signed and retailed by other opticians, such as Bate, and Dollond. It would appear that Hugh Powell started signing some of his own instruments in 1840, and a few examples exist which still feature his early fine adjustment, which worked through a wedge under the stage, and this less-satisfactory arrangement was later abandoned.

In 1840, the newly formed Microscopical Society commissioned Messrs Hugh Powell, Andrew Ross, and James Smith each to furnish a standard instrument made to their own peculiar views. Powell s massive model(left) as delivered to the Society is still part of the R.M.S. collection today, and features a solid triangular post, as well as the first example of an English microscope equipped of an achromatic condenser. A small number of this large model continued to be made until 1849.

Sometime in late 1841 Powell took into partnership his brother-in-law Peter Lealand, thus forming the famous firm of Powell & Lealand. Their first joint venture was to bring out a different large microscope based on the Jackson optical-bench principle, which featured a conical fine-adjustment mechanism, which carried the weight of the upper body and tube, and as such was prone to wear. This model, shown to the right, was illustrated in Daniel Cooper s: The Microscopic Journal and Structural Record for 1841, and later published as a separate brochure by Messrs Powell & Lealand in 1842. Descriptions of the microscope are also found in other sources. In a later version of the instrument, the fine-focus arrangement has reverted to nose-piece adjustment. It would appear that at this stage Powell & Lealand were also still manufacturing for the trade, as examples of their work are known signed and retailed by others, including Carpenter & Westley, and Dollond.

In 1843 Powell & Lealand came out with a radically new design on the bar-limb principle, combined with a tripod foot. An example of this 'New Microscope' from the first year of its production is now on this site. This coincides with the appearance of Andrew Ross s first bar-limb design microscope, but the tripod foot, which resembled a kettle-drum, was a distinct Powell & Lealand feature. This was described in that year s November issue of The London Physiological Journal as Powell & Lealand s new microscope . In this, the microscope is supported by tripod legs, and small rounded feet, which carry the body on trunnions, and there is a transverse arm which contains the long lever, which moves the nose-piece fine motion. In the initial design, the fine-focus screw, which was attached to a cone, was placed on the right side. In 1847 this was moved to the familiar vertical position on the top of the arm, immediately behind its pivot.

Coinciding with this development, a portable version of this model appeared, with folding feet, allowing the instrument to be packed neatly in a compact box. This was later known as the 'portable' or No 4 model(right), and the original design became known as the No 3 model. At this stage, the microscope tube was also supported by a set of diagonal stabilizing struts extending from the back of the arm to the upper third of the tube. Sometime during the early-1860s these were abandoned.

In 1848, a student model was developed, later referred to as 'The Iron Microscope' (left). This had an off-set pillar and flat tripod stand, a single coarse-adjustment milled head placed on the right, and a lever-operated stage as designed by Alfred White. Some examples of this instrument had a foot wholly made in brass, and some were signed by other retailers, such as Carpenter & Westley. This model continued to be made until the first decade of the 20th Century, and was later known as their No 5 or Student Model.

Powell & Lealand did not enter the 1851 Great Exhibition, but it is believed that during this time they worked on a larger model based on their 1843 tripod design. Dated examples are extant from this period, including two on this site, which have the more solid rectangular legs and feet as in the later No 1 and 2 designs, either with or without the supporting struts. These could be regarded as the proto-No 1/No 2 stands , from which the later models were developed.

The next model(right) was worked on at odd times and appeared in 1861. It was similar in outline and appearance as the final No 1 design, save for the massive ring attached to the limb, within which there was a second ring carrying the stage and substage assembly, allowing both to be rotated with the same rack-and-pinion movement, and separate rotation also provided for the substage. This model continued to be made until the definitive version of the No 1 model stand was put on the market in 1869.

The main modifications made from 1869 on were in the construction of the rotating stage, which this time was mounted in the same plane as the ring, and there was a separate carrier for the centering and rotating substage, attached below the stage now, and not rotating with it as in the previous model. In this form, the Powell & Lealand No 1 microscope continued to be made largely unchanged for another 40 years. The only additions were a fine adjustment to the substage (1882), rack work to the monocular draw tube (1887), and diagonal rack work to the coarse adjustment, all at the suggestion of E.M. Nelson, an eminent microscopist, and loyal user of this model.

E.M. Nelson

Alongside the No 1 model stand, Powell & Lealand developed another, slightly smaller model, known as their No 2 (left). This differed from their No 1 in four respects: Instead of 1 inch, it had inch X and Y motion to the stage; instead of a rotating stage, it had a sliding and rotating object holder; the stage plates were not graduated; and when inclined horizontally, the eye point was a distance of less than 10 inches from the table surface. It did feature the same centering and rotating substage as on the No 1.

In addition, Powell & Lealand continued to produce their original design with the ranker tripod foot, now designated their No 3 stand(right). This differed from the No 2 in that it was smaller again, had no rotary movement to the substage, and instead of rectangular mechanical movements to the substage it had mechanical eccentric centering movements.

As a firm, Powell & Lealand were always small, and remained a family business, with Hugh Powell s son, Thomas (1833-1925), being an active member of the team, and taking over after his death in 1883. Hugh Powell alone worked at 24 Clarendon Street, Somers Town, London from 1832 to 1842 when Peter Lealand joined him. They subsequently moved to Seymour Place, Euston Square, London, where they were located from 1846-1857, and from 170 Euston Road, London (same premises), from 1857-1905. In later years, Thomas was almost solely involved in the production of the microscope objectives, and it was reported that he worked in great secrecy, always covering his work before the entrance of visitors. Dr Henri Van Heurck, in his well-known text The Microscope , says of the firm: Messrs. Powell & Lealand occupy quite a unique position in the microscopic world. Their workshops are small, the number of instruments which they produce are few, but every piece of apparatus, marked with their name, is an artistic production, perfect in all its details. Moreover, both instruments and objectives of these makers are in the greatest request, and are used in England by all serious microscopists .

Towards the end of the 19th Century, competition from German firms, such as Zeiss and Leitz, with their mass-production techniques, and apochromatic objectives, which could be produced less expensively, caused demand for Powell & Lealand s products, which largely catered to the wealthy amateur, to fall. In the end, there were only a few staff left, including Thomas Powell, and Mr Lealand junior, alongside foreman Charles Perry. After Powell & Lealand ceased making for themselves, a number of stands were sold by Swift, under supervision from Charles Perry. He later moved to work for C. Baker in 1904, and made No 1 stands to be approved by Thomas Powell until 1914. Perry also made the Baker Curties-Nelson No. 1a, which, not surprisingly, used a stage virtually identical to the one used on the Powell & Lealand No 1. At that time, the address of the firm was given as Elmstdale, 87 Greenham Road, Muswell Hill, London. Thomas Powell continued to service and repair his instruments almost to his death, in 1925.

HISTORY OF POWELL & LEALAND OBJECTIVES:

Hugh Powell, whilst working for the trade, must have started making microscope objectives in the mid-1830s. He was a pioneer in the production of very high powers in objective lens systems, and made a 1/16-inch objective as early as 1840. His son Thomas followed this tradition, by making a 1/25-inch dry objective in 1860, and a 1/50-inch in 1864, for Dr Lionel Beale. Dr Beale persuaded him to make the even more remarkable 1/80 objective in 1872, which Beale mentions in his 5th Edition of How to work with the microscope (1880). As far as is known, this is the only example in existence.

It must be mentioned that at this stage there was still no knowledge of Abbe s theory of diffraction, and the associated concept of numerical aperture (N.A.), a measure of the resolving power of objectives. This dictates that as a measure of resolution:

       N.A. = sin α x R.I. (refractive index of the medium)

       α being half the angular aperture. For air, the R.I. is 1.0, for water 1.33, and for modern immersion oil 1.515.

The early microscopists, and especially the lite of rich English amateurs, who amused themselves by resolving the fine details of test objects such as diatoms (scathingly known as diatom-dotters ), strived to acquire objectives with greater and greater angular aperture, at that stage not realising they were really chasing an asymptote. For instance, the gain in resolving power of a 175 over a 160 objective is negligible, considering their respective N.A.s are 0.98 and 0.999!

The immersion principle had been experimented with earlier by David Brewster, and the Italian professor Giovanni Battista Amici, who demonstrated a water-immersion objective at the Paris Exhibition in 1855. At first, it was not realised that immersion would increase the effective aperture, and the prevailing thought at that time was that it only tended to reduce the loss of light through the air-glass interface. This theory was also supported in England, especially by authorities such as Francis Wenham. However, on the Continent, more interest was shown by opticians, including Edmund Hartnack (1826-1891), and Friedrich Adolf Nobert (1806-1881). Hartnack impressed the judges at the London Exhibition of 1862 with his water-immersion objectives, which were better than Continental dry objectives in resolution. It is thought that the superiority of Powell & Lealand s dry objectives, such as their 1/25 inch, which were about equal in resolution as Hartnack s immersion, caused it to take longer for the score to be settled in favour of immersion objectives, such as was finally demonstrated by the microscopist John Mayall (1842-1891).

Spurred by this new evidence, Powell & Lealand produced their first water immersion in 1869, an 1/16-inch objective. Water immersion was at this stage available as an optional extra for their high-power objectives, in the form of immersion fronts , which replace the dry front lens, simply by unscrewing and replacing one with the other. The 1871 catalogue lists this arrangement for the 1/8, 1/12, and 1/16-inch objectives. The 1875 catalogue adds this feature also for the -inch 140 objective.

In the USA, Robert Tolles had experimented initially with water immersion, but in about 1873 he produced a 1/10-inch objective using soft Canada balsam as an immersion medium, which had an aperture of 110 , equivalent to an N.A. of 1.25, but was less than practical, due to the viscosity of the balsam. Around this time, Ernst Abbe followed up on the idea of homogenous immersion generated by Stephenson, and published his famous paper in the Journal of the Royal Microscopical Society in 1879. Instead of water, a drop of oil with the same refractive index of glass (about 1.52) was placed between the front lens of the objective and the cover glass, taking the theoretically possible maximum N.A. up to this number. Not long after, Powell & Lealand produced their first oil-immersion objectives, commencing with a 1/12 inch with an N.A. of 1.20, followed by a 1/25 inch of 1.38, and even a 1/50 inch with the same resolution. A 1/12 inch with a hyper-hemispherical front lens with an N.A. of 1.43 followed in 1880, and 5 years later, they came out with their oil immersions of 1/8, 1/12, and 1/50 inch, all with flint-glass front elements of a higher refractive index, producing a remarkable N.A. of 1.50, close to the theoretical maximum. Despite the high N.A., these lenses were not very practical, as they were less well-corrected, suffered from very short working distances, and especially the 1/50 inch produced only empty magnification , which revealed no additional detail.

A further development in microscope optical design was the appearance of apochromatic objectives in the early 1880s through the work of Ernst Abbe of Zeiss, using the new Schott optical glass, which had lower dispersion properties, and allowed correction for three (blue, green, and red) colours instead of two (blue and red), as in the achromatic lens combinations. As they were over-corrected for some colours, they were to be used with compensating eyepieces, which counteracted this. In 1882, an addition to the substage, was the substage fine focus mechanism to facilitate 'Critical Illumination' at high power.

About 1892, Powell & Lealand started manufacturing their own apochromatic objectives, using Jena glass, and made some remarkable objectives including oil immersions of 1/8, 1/10, 1/12, 1/20-inch focal lengths, with N.A.s of 1.40, and even 1/10, 1/12, and 1/20-inch objectives, each with an N.A. of 1.50. Naturally, these were expensive, and ranged in price from 20 to 50. Unfortunately, the earlier Schott glass proved unstable, causing de-vitrification, rendering the lenses opaque, and today few, if any, of these objectives are still in useable condition.

Towards the end of the 19th Century, the small firm of Powell & Lealand, even in England, had started to suffer from the competition from the German makers of apochromatic objectives, and their catalogues of 1896 and 1899 suggest they lowered their prices substantially. They even advertised a new apochromatic 1/12-inch objective with an N.A. of 1.40 for only 10, with the addition: This objective is a rapid photographer . Alongside this, they made a dry and an oil-immersion apochromatic condenser. After they ceased trading in 1901, for some time their objectives continued to be advertised by other makers, such as W. Watson & Sons in their 1902 catalogue, before this firm started making their own apochromatic lenses.