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:
CLICK ON IMAGE FOR LARGER VIEW
CLICK 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.
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
Asparagus
Willow oak root
N4 next + To be filled at Pleasure'
The
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 ..glass 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.
REGARDING THE SIZE OF THIS INSTRUMENT:
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
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.
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.
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.
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.