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THE POWELL & LEALAND No 1

MAKER: POWELL & LEALAND

DATED: 1874

SIGNED ON THE ARM: Powell & Lealand, 170 Euston Road, London and also dated 1874

Authors: Jurriaan de Groot & Barry Sobel

Editor: Joseph Zeligs

Please Click On Any Picture for a Larger Version

INTRODUCTION:
This page is about a monocular example of the famous Powell & Lealand No.1 stand, regarded by many as the ultimate example of the microscope-maker's art and skill, the Aristocrat of the Victorian period of brass and glass. Even without the accessories, the P & L No.1 was so expensive, that only the wealthy could afford to buy one on their own. Although this example lacks many accessories and its case, there is a description of a binocular example, complete with case and accessories also on this site.

DESCRIPTION:
This microscope arises from a massive English Tripod foot with a span of about 7 x 9 inches, with each toe of rectangular profile. The body is suspended on trunnions. The trunnion support is close to the table, allowing for a low center of gravity, which is necessary to produce a high level of stability when the instrument is positioned in either a highly inclined or horizontal position. The microscope would be placed in a very inclined position for direct use of an oil lamp for illumination (without the mirror) during use of high powers, and horizontally for drawing using the camera lucida, bringing the eye of the observer to about 10 inches (250 mm) above the table, this being considered equal to the point of comfortable near vision.

Coarse focusing is by straight cut rack and pinion, which is sprung, and can be adjusted for wear. The rack is attached to a solid bar which has a slightly trapezoidal shape in cross section. Attached to this bar is the arm which holds the body tube. The tube can be turned to the side clockwise. It registers on an adjustible stop on the bottom the arm. Fine focusing is by a micrometer screw acting on a long lever running through the arm, and acting on the sliding nose piece, whereby one turn of the screw represents 0.16 mm of vertical displacement. The fine focus knob is divided into 20 parts, each therefore representing 0.008 mm of vertical movement, labeled every 5. The microscope is signed on the arm: Powell & Lealand, 170, Euston Road, London*, and dated just behind the fine adjustment screw, 1874

*The adjustments on better quality microscopes have tension applied to them via spring mechanisms which ensure accurate and firm engagement of the parts such as pinions to the racks and other contact points.

The Turrell stage is operated through concentric knurled knobs, allowing for a movement of 1 inch across the X and Y axes, which can be tracked on specimen-finder scales graduated 0-100. The scale for the X-axis is lacquered brass and the scale for the Y-axis has a more copper-colored hue. The stage can be rotated through a full circle, graduated on a scale 0 to 180 to 0 by both 0.5 and also single degrees, labeled every 10 degrees. The graduations for rotation are on a lacquered brass plate, unlike many of the later examples which employed a platinum plate (also found on the Nelson No 1a which has an identical stage rotation. The rotating motion is operated through a conical rack and pinion movement with a diagonally placed knurled knob under the stage on the right side. Although this is constantly engaged, the stage can still be rotated manually. The slide rests can be moved back and forth; the front one has spring-loaded slide contacts. The mechanical stage mechanism remained the same for many years. The Y-axis(forward/backward) motion is by rack and pinion, and the X-axis(right-left) motion is by a wormscrew-like device known as a 'constant lead cylindrical (or barrel) cam' acting on the 'follower', shown in detail on the page illustrating this mechanism on the original P and L model of 1843. There is a group of screws on the back of the limb which provide a facility to center the stage. The centering process, making use of these screws, is still a tedious undertaking, and the stage was likely intended to stay centered once it left the factory.

The substage mount(left), is focussed by rack and pinion, and can be centered by a pair of screws set at right angles (range about 3 mm for X and Y axes); it features full circular movement, activated by a diagonally placed knurled knob. It also has the addition of the substage fine focus(right), to facilitate precise focusing of the condenser at high power. This substage fine focus uses a cone to move the secondary vertical movement. This is an upgrade, (suggested by E. M. Nelson) added later, since this feature was not added to P & L's No 1 microscopes until 1882*.

*JRMS 1882,pp554-555.

The top of the substage housing(left) has two concentric sleeves. The inner sleeve rotation is activated by a knurled knob while the outer sleeve is fixed. A polarizer can fit into the inner sleeve either at the top or bottom.
As shown to the right, when a polarizer is inserted from the bottom, this allows a set of selenites to fit into the outer fixed sleeve on top(right) so the polarizer can be rotated while the selenites remain undisturbed. This arrangement is discussed further below.

The large plano concave mirror is 3 inches in diameter, and is on a double articulated arm attached to a collar running on the tail piece of the lower limb with a knurled knob to clamp it in position. The mirror is carried by the signature P & L single- sided arc attachment. This type of unilateral attachment, a sort of hemi-gimbal, is also found on the Baker company's Nelson-Curties No 1a stand.

The body tube is monocular. It has a manual draw tube calibrated 0 to 4 inches, in 1/10 inch increments labeled every inch. There is an RMS thread at the bottom of the draw tube. This could accept an erecting lens, or be used for a special lens to view the rear objective plane when measuring numerical aperture or viewing conoscopic figures. This movement of the draw tube changed from manual to rack and pinion in 1887, after being suggested by E.M. Nelson.

ACCESSORIES:

EYEPIECES

The signed P & L eyepiece has a diameter of 1.32 inch (= 33.5 mm), not the same size as the push-in fit for the substage mount, nor the main optical tube. This eyepiece has the same diameter as some, but not all, No 2 Stand eyepieces and is likely a No 2 eyepiece adapted to this No 1 stand. In order for this P & L eyepiece, made later than the microscope, to fit the optical tube, an adapter is provided of 1.435 inches(36.4 mm) outer diameter. The eyepiece is signed POWELL & LEALAND and with the number 5. This likely indicates it is a 5X eyepiece.

There is also an unsigned Ramsden-type filar screw micrometer eyepiece which fits the microscope tube and is fully functional with intact filaments.

OBJECTIVES:
There are currently a total of 10 objectives, 9 by P & L with this microscope. All of the P & L objectives have correction collars except for the one inch. The 2 inch objective is by Ross in its original can. Most of the Powell & Lealand objectives are signed Powell & Lealand, with the exception of the one inch. The water immersion 1/4, the 1/12 apochromatic oil immersion, and the 1/50 all have their purported n.a. inscribed on them. Only the 1/50 has its focal length inscribed on the objective. The 1/50 has delamination of the rear elements. The 1/12 inch has delamination only at the edges of the rear elements. There is a P & L Lieberkuhn for the 1/4 inch P & L dry objective. The images taken through the objectives were taken on the P & L microscope using an adapter accepting the Omax 5MP microscope camera fitted to the top of the optical tube.

P and L obj

Click on a picture to see more images and details, if available.
FOCAL LENGTH(In.)	MAGNIFICATION	N.A.	ANGULAR APERTURE	COMMENTS
2 INCH (ROSS)	5	0.27	32^o	Proboscis of Blowfly
1 INCH	10	0.33	38^o	Trichrome stain, human kidney
1/2 INCH IN ORIG. CAN	22	0.50	60^o	Trichrome stain, human kidney
1/4 INCH IN ORIG. CAN	40	0.63	78^o	Trichrome stain, human kidney
1/4 INCH WAT IMM	40	1.0 (labelled 1.12)	90^o	Trichrome stain, human kidney
1/5 IN ORIG. CAN	50	0.80	108^o
1/8 IN ORIG. CAN	96	0.9	130^o	Trichrome stain, human kidney A high power dry objective with correction collar.
1/12 IN ORIG. CAN	120	1.40	137^o	This objective and its can are both engraved with a n.a. of 1.40, the objective is serial numbered N^o98. This objective was noted to be New in the December 1894 P & L catalog of Apochromatic Objectives, hence this example must date to after 1894.
1/16 INCH IN ORIG. CAN	160*	?	^o
1/50 INCH OIL IMMERSION IN ORIG. CAN	500*	1.38	134^o	Serial number 1. c.1880

This is mostly empty magnification*

The 1/50 oil immersion objective is signed Powell & Lealand both on its proximal part as well as its distal part. It is also signed with its serial number of N^o 1 and its n.a. of 1.38. The original can is also signed Powell & Lealand, ¹/₅₀, Oil Immersion, N.A. 1.38, London. Unlike the other objectives, the signature on this objective is in block letters rather than script. According to Seville Bradbury this objective was first made in 1880. In the 1893 catalog, the 1/50th oil immersion achromat was priced at £80; in 2022 this would be over £11,426 or around $12,797 US. Its very short focal length would make using it very difficult. This example has severe delamination of its rear elements, making it unusable in any case.

CONDENSERS:
The microscope includes Powell & Lealand’s well known Improved High Power Achromatic Condenser, with a wheel of 11 apertures, and 4 darkground stops, as well as a round stop at the end of rotation that can be used to create variable amounts of oblique lighting. The aperture wheel and stop train are operated by separate arms and pointers, the stops recording positions from 0 to 4 on a dial. The different size apertures are indicated by numbers shown on the front of the condenser. The condenser can be used for high power with its top element on, or with the top element removed, as a moderate power condenser for objectives with focal lengths as long as one inch. This example has a reported angular aperture of 170^o, and an n.a. of 0.99. It was NOT designed for use with oil immersion objectives, which did not exist when it was first designed. This type of condenser was quite popular and larger examples which fit the two inch substage of i.e. some Ross Microscopes, were also made by Powell & Lealand.
There is also a Wenham-Shadbolt paraboloid(right) with a central stop, the height of which can be varied by its screw controlled from the bottom.

An additional adapted Watson Holos Oil Immersion Condenser with Iris diaphragm has been added to allow proper homogenous immersion illumination. This condenser has a labeled n.a. of 1.3.

Another Powell & Lealand condenser fitting with the microscope is the special Oil Immersion Condenser fitting with Sliding Tube arrangement for stops. This arrangement allows the focus of the condenser to remain unchanged while the individual stops are changed. This example is fitted with a Watson Holos Oil Immersion Condenser. This condeneser fitting could also be supplied with an apochromatic optical part. The P & L Apo condenser fitting was also sold by Watson as listed in their 1896 catalog.

POLARIZED LIGHT ACCESSORIES:
These include an large calcite prism Polarizer and a Powell & Lealand type nosepiece analyzer (images to the left), as well as a fitting which houses three selenites(images to the right). The large polarizer fits up into the substage assembly from below. The polarizer can be rotated via the brass knurled knob of the substage housing. The set of selenites fits into the outer ring of the top of the substage. Each selenite can be swiveled into or out of the optical axis, either individually or together with one or both of the others. Each of the selenites is labeled on their underside, as this is easier to visualize from below when they are are installed on the top of the substage. Each selenite is labeled P|N, indicating its primary axis, and each is further labeled with its waveplate retardation: 1/4, 3/4 or 9/4 wavelengths, respectively. Each selenite may be rotated individually via a knurled edge on each of the three housings. The selenite housing is threaded on top to accept the Powell & Lealand the Apochromatic High Power Condenser optics or the Powell & Lealand achromatic Condenser Optics.
larger sizes to fit i.e. Ross microscope substages.

OTHER ACCESSORIES:

A silvered nosepiece-mounted side reflector, although unsigned, is the type sold by Swift.

A signed Powell & Lealand Vertical Illluminator uses a glass plate, fixed at 45^o as a reflector.

A signed Swift-brand Davis shutter for the nosepiece for dark ground work is included.

Another accessory is the Varley-type live box. This device provides a glass tablet upon which small microscopic lifeforms, e.g. in pondwater, may be viewed, covered with a cap which includes a glass cover. The Varley type of live box has a channel around the tablet which provides a reservoir of liquid which, by capillary action, can keep the subject moist.

Along with the microscope is a Amici Prism Lenticular illuminator on stand for substage oblique illumination.

CONDITION:
This microscope is in sound mechanical condition. All controls work as they should. The fine focus screw is slightly bent, but works normally. There are scattered lacquer losses throughout as can be seen in the images, but no pitting of the lacquer, or severe disfiguring losses in my opinion. As noted, there has been a modification after initial construction, adding the substage fine focus assembly, which has an oxidized blackish finish in very good condition. This addition was probably not done by P & L themselves as the fitting was not properly centered, the screw holes being placed incorrectly when I received it. To correct this required enlarging the holes in the directions needed, and the mechanism is now correctly centered.
Although stage rotation is very smooth, the stage is not perfectly centered, the adjustment mechanism for this quite complex and difficult to adjust; I have not yet attempted to perfectly center the rotation of the stage. The top of the selenite housing has 3 threaded holes drilled into it which would have held a plate with a central threadnfor adapting a different condenser. The large polarizer has two tiny threaded holes on the knurled bottom disk. The original can is lacking for the water immersion 1/4 inch objective. The 1 inch is unsigned but by P & L and is in a signed P & L can. The 1/12 oil immersion objective has slight delamination around the edge of the rear elements. The 1/50 inch objective is severely delaminated at the rear elements but contains all lenses. All the objectives are in very good cosmetic condition.

HISTORY:
History of the P & L No 1 microscope is detailed on the page about a binocular example.

In regard to P and L objectives, the history of the oil immersion objectives made by them is not well known. While Zeiss constructed their first oil immersion lenses in 1878, P & L produced their first, a 1/8 inch oil immersion objective in 1879, and subsequent oil immersion achromats in the 1880s. In the JRMS of 1880 on page 524, an oil immersion 1/25th by P & L with an N.A. of 1.26 is reported. In the JRMS of 1881, it was reported on page 714 that P & L produced a 1/8 with an N.A. of 1.4 that year. Oil immersion objectives by P & L are not mentioned in the JRMS starting about 1886 when their first apochromat was discussed. Unfortunately, there are no catalogs or price lists known from the years of 1880 through 1892. In the catalogs from 1893 and 1895, oil immersion achromats are listed and range from 1/8 inch focal length to 1/50. In the December 1894 catalog of apochromats, the 1/12 oil immersion obective with a n.a. of 1.40, an example of which is seen on this page, was listed as NEW. In both the 1893 and 1895 catalogs, the N.A. of the 1/50 is listed as 1.33, slightly lower than the 1.38 listed on the 1/50 oil objective seen on this page, and serial numbered 1. According to Seville Bradbury, the oil immersion 1/50 was first made in 1880, but so far, I have found no other reference that dates it, and it is apparently not mentioned in the JRMS.

Starting in 1886, P & L tried to compete with Zeiss producing a range of apochromatic lenses, including oil immersion apochromats which seemed to soon overshadow even the achromatic oil immersion objectives. The literature of the time also seems to have little to say about the highest power P & L oil immersion achromatic lenses. In any case, objectives with shorter focal lengths, and therefore higher magnification that do not have higher n.a.'s, will not provide any useful improvement in resolution over lower powered but equal n.a. objectives, and this may be the reason for the lack of discussion in the literature of these objectives such as the very rare 1/50th oil immersion achromatic objective mentioned above.