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SCREWBARREL MICROSCOPE (Wilson-Hartsoeker Type):

c. 1725-1750, unsigned


Screwbarrel Microscope1

screwbarrel microscope

screwbarrel microscope

screwbarrel microscope

screwbarrel Microscope

screwbarrel microscope

screwbarrel microscope


This is a small screwbarrel microscope. It is a smaller version of the type popularized by James Wilson, and is one of the earliest microscopes in this collection, being one of the few dating to the 18th century.   The kit is housed in a fishskin-covered wooden case lined with dark-green thin velvet, with the padded inside lid lined with thin green silk or velvet. This kit is identical to number 268 in 'The Great Age of the Microscope' by G. Turner.   The case measures only 3 7/8 X 2 3/8 X 1 1/2 inches.   The kit, fairly complete, includes:
  1. The Microscope, made of lacquered brass.
  2. The original four ivory sliders (with a few specimens missing)
  3. A handwritten list of objects in the 4 sliders
  4. A 'talc box' containing brass circlips inside one end and mica 'talcs' inside the other (both sides full)
  5. A small brass forceps with very sharp points
  6. A brass & glass live-box, or 'wet cell' slide with three glass wells and a (relatively thick) coverglass
  7. The original three eyepiece lenses, numbered 1, 2 and 3. There are brass lens caps for two of the three, the third lens is stored on the microscope.

screwbarrel with slideCLICK ON IMAGE FOR LARGER VIEW

screwbarrel with vialCLICK ON IMAGE FOR LARGER VIEW

The case closes with two brass catches. The lenses are numbered 1 to 3, in decreasing order of magnification (i.e. the higher the number, the lower the magnification). The lenses are not parfocal and considerable travel in focus is needed to achieve a sharp image after changing lenses. The condenser "lens" is large, i.e. nearly the diameter of the 'screw' end, and it is screwed into the far end of the instrument.   In use, the far end is turned and presses against the stage which in turn is held in place by a spring between the eyepiece and the Bonanni stage. The Bonanni stage consists of three plates, held together and around the slider or other object-holder, by the spring putting pressure on the plates from above. The sliders and the live box slide have a tapered end which makes it easier to insert them between the upper two plates of the stage. The upper two stage plates each have a partial opening on the sides between them to facilitate insertion of the sliders. A glass vial can be inserted between the lower two plates to examine the circulation of a (e.g.) a newt. There is a V-shaped bend in the center of the bottom plate to prevent the vial from moving during observations. The microscope measures about one inch in diameter and two inches in length when in the usable focused position for an observation; it is about one and three-quarters inches long when the barrel is screwed into to its maximal depth, moving the slider closest to the eyepiece.

sliderslider The live box slider, or 'wet-cell' slide, consists of three parts. The outer casing holds the other two parts together and has a tapered end to make inserting it in the sprung stage easier. There are three concave glass wells. Liquid samples of pond water, for example, would be placed in these, covered with the other piece of glass and the two inserted together into the outer brass casing. The outer casing holds the other two together well. Although the cover glass appears irregular, it is still large enough to cover all three wells at once.

The bone or ivory sliders appear to all be original and the list of objects matches the objects on the sliders (except of course for the fourth which was supplied empty and to be filled with objects at the owners convenience and discretion). The handwriting on the list matches the handwriting on the sliders. In addition, the mica 'talcs' and circlips in the talc box fit the slides perfectly.   As noted on the handwritten list:


'A List of objects in 3 Sliders:

N1 next +   Feathers of a moth
                    Farina of Holyoak
                    Dust of Poppy seed
                    Seed Vessels of sorral

N2 next +   Wing of Stone fly
                    Ditto of a Libella
                    Ditto of a Gnat
                    Ditto of a Locust

N3 next +   Virgins Bower
                    oak root

N4 next +   To be filled at Pleasure'

screwbarrel slides

screwThe image to the left is from John Cuff's 'THE DESCRIPTION OF A POCKET MICROFCOPE WITH THE APPARATUS THEREUNTO BELONGING As made by John Cuff.'     The description that follows is Cuff's but I have abridged it and used the modern 's' for the archaic 'f' sounding like 's'.   I also substituted the word 'Talc' for the archaic spelling of 'Talk':

AB Represents the Body of the Microscope...CC, a long fine-thread male Screw, that turns into the Body of the Microscope. D, A convex glass at the End of the said Screw, to collect the Rays of Light, and point them upon an object... EE, Three thin Plates of Brass within the Body of the Microscope, one whereof is bent semi-circularly in the Middle, so as to form an arched Cavity for the Reception of a Tube of Glass...G, The other End of the Microscope, where a hollow female Screw is adapted to receive the different Magnifiers...H, A spiral Spring of Steel or Brass between the said End G and the Plates of Brass, intended to keep the Plates in a due Position, and counteract against the long Screw CC. I, a small turn'd Handle for the better holding of the Instrument, to screw on or off at pleasure. To this microscope belong ...different magnifying Glasses...observe the lowest Numbers are the greatest Magnifiers...M is a flat Slip of Ivory, call'd a slider, with four round Holes thro'it, wherein to place Objects between two Glasses or Talcs... such Ivory Sliders and one of Brass usually go along with this microscope... The Ivory Sliders sold herewith are numbered, and contain the Objects following. Begin with the Hole in each Slider next the +... The Brass Slider is to confine any small living Object, that it may be view'd without crushing or destroying it...N, Is a forceps or pair of Plyers, for the taking up of Insects, or other objects, and adjusting them in the Glasses. O, A little Hair Brush or Pencil, wherewith to put upon the Talcs or any small Drop of Liquid one would examine. When you design to view an Object, thrust the Ivory slider (in which the object is placed) between the two flat Brass Plates, EE, observing always to put that Side of the Slider where the Brass Rings are, farthest from your Eye: The screw in the Magnifying glass you intend to use at the End of the Instrument G, and looking thro' it against the Light, turn the long Screw CC till your Object is brought to the true focal Distance: which you will know by its then appearing perfectly clear and distinct. The Way of examining any Object accurately, is to look at it first through a Magnifier that will shew the Whole thereof at once, and afterwards to inspect the several parts more particularly with one of the greatest magnifiers: For thus you will gain a true idea of the Whole, and of all its Parts...As the Object must be brought very near the Glasses when you employ the greatest Magnifiers, be particularly careful not to let your Slider rub against them as you move it in or out, least you scratch and spoil your glasses: This easily may be prevented by a few turns of the Screw CC which will give you room enough... P, Is a Tube of Glass contrived to confine living Objects, in order to discover the Blood, as it streams along the Veins and Arteries...The best Light for viewing Objects, is a clear Sky-Light, the Sun shining on any white Thing, or the reflection of its rays from a Looking glass: Candle light is also good; but People not much practiced in Microscopes find it somewhat difficult to hit the candle exactly. But whatever Light you use, be very careful not to shade the Object by your Hat or Periwig, for the best of Glasses can shew but little, unless the object be at a just Distance, and have a sufficient Light... The single Microscope above described may be formed into a double one, by screwing to it a Tube with an Eye Glass at the End thereof. Also the Addition of a particular Apparatus contrived by Mr Cuff for that Purpose, it composes the best kind of Solar Microscope;... for this Way, a Louse may be magnified to the Length of 2,3,4, or 5 Feet...'

Cuff then went on to describe his compass microscope with Lieberkuhns for viewing opaque objects; unlike other makers who made attachments for the Screwbarrel for use with opaque objects (as shown in the last paragraph of this web page), Cuff stuck with the Lieberkuhn-equipped compass microscope for this purpose. This makes some sense for high powers where the use of an ordinary lens will not work satisfactorily. Cuff started to make Lieberkuhn-fitted microscopes about 1738.


compare screwbarrel scopescaption

When I first obtained this instrument, and for some years afterwards, I thought this was likely the smallest example of a screwbarrel microscope. Although small, and certainly smaller than the ones with provision for a handle, it is not the smallest. Through the kindness of some fellow collectors, I am able to provide the reader with a visual comparison. This would then make mine, despite being quite small, about 'mid-sized' when it comes to known examples of screwbarrel microscopes. The example second from the left has a blackened-ivory shade over the condenser end to prevent oblique light from entering. Interestingly, even that little example that is second from the left still came with a full complement of accessories including glass vials and an offset attachment for viewing opaque objects. For more about this type of offset accessory, see the last paragraph and engraving at the bottom of this web page.

HISTORY OF THE SCREWBARREL MICROSCOPE campani microscopetortonus screwbarrel

The screwbarrel microscope has some features that can be traced back to prior makers. Use of the screw focusing mechanism for the main body of the microscope was used in compound instruments of the 17th century including the Italians Divini and Campani(left) (mid-1600's onward) and even John Yarwell of England in the late 1600's.

A compound form of portable handheld screwbarrel microscope was first invented by Carlos Tortoni (Tortona, Tortonus) of Italy, announcing this in 1685; his original drawings are shown to the right. According to Clay & Court, Tortoni first described his microscope at a meeting of the Accademia Physico-Mathematica held in the house of Lord Camp (sic Ciampini) at Rome on August 5, 1685. According to Clay and Court, the tube was 2 inches long. It was composed of five parts, each joined by a screw to the succeeding part, and it could be divided into a microscope and an eyeglass; this was illustrated in his instructions for the use of the instrument: Instruzione delle Due Sorti di Microscopi Tortoniani Nuovamente Inventati e dati in luce (image of his illustration shown to the right). Tortoni's (Tortona's) account is also in Acta Eruditorum(1685 p478) and in other publications. (Also see: History of the Microscope, by Clay and Court 1932, reprinted by the Holland Press in 1975 p. 41). Both the Tortoni invention, and Bonanni's modification (see below) were compound microscopes.

bonanni The use of a sprung stage with pressure plates can be traced back to Bonanni, who incorporated it into one of his compound screwbarrel microscopes(left) in 1691.

hs screwbarrel hs2 It was Nicolas Hartsoeker who, in the 1690's, first used the screwbarrel design for a simple microscope(left) and he incorporated a condenser, similar to the later model of James Wilson (about 1702,(right) and also Edmund Culpeper. Although Wilson is often credited as being the first to introduce the Screwbarrel microscope to England and his first known illustration of it dates to 1702, some examples of Culpeper's screwbarrel microscope which are signed and dated, have their signed date as early as the year 1700. Hartsoeker's condenser could be focused, using a screw mechanism separate from the focusing for the eye-lens, whereas the condenser lens in Wilson's instrument (and mine) are fixed and had to move as a unit with the stage as the stage was brought closer or further away from the eyepiece. The glass at the end of the microscope at the top of this page is plain glass and not a true condenser. Clay and Court claim that the lenses that Wilson used were superior to those of Hartsoeker. In the larger version of the Wilson Screwbarrel microscope, unlike Hartsoeker's, there is provision for a handle to be attached to the side of the barrel of the microscope, as shown in the images of Cuff's example above.

screwbarrel with opaque attachement The reader may note that my little screwbarrel microscope has no provision for viewing opaque objects.   Wilson initially provided separate 'compass' microscopes for this purpose, but about 1710 he introduced an accessory for the screwbarrel for this purpose, as shown to the left. Simply, this consisted of a little arm that screwed into the end of the screwbarrel where the eyepiece would be, and the eyepiece was instead screwed to the end of this offset arm. He provided a specimen holder that was inserted through the spring stage that would stick out to be positioned under the offset eyepiece, thereby allowing lighting of an opaque object from the side. Focusing was then still accomplished by turning the microscope screw. Wilson simply fit a thin spike in the groove of the screwbarrel stage, but this is not very stable. Soon after, Culpeper invented a better method that supported the forceps or black and white disk via a brass slider to which the spike was attached, carrying a forceps on one side and a disk on the other. As noted above, Cuff was among the first in England to use a Lieberkuhn-equipped 'compass' microscope for opaque objects. It is generally believed he started this practice about 1738 as a result of his contact with Lieberkuhn.

The author is grateful to Howard Lynk for help in deciphering the "old English" script on the slide list and to James Solliday and Dr. Joseph Zeligs, for helpful suggestions.