apparently, double-convex and plano-convex. The last three have diameters of
about 14. The distance between the four lenses is 75 and the eye aperture is just
over 1 mm.
The Van Deijls were well known for the quality of their optical instruments,
Jan lived c. 1715—1801, and his son, Harmanus, 1738—1809.
Rooseboom (1940b); Engberts (1970), describes five telescopes by Van Deijl in
Leyden.
Inv. yo/3
264 ACHROMATIC TELESCOPE 1781 (35S Fig. 227
Telescope by Jan and Harmanus van Deijl, Amsterdam
Signed around the objective mount: Jan van Deijl & Jjoon Fecit Amsterdam
A° 1781
Stand by J. Kampman and Adam Steitz, Amsterdam
Height to pivot 1,400, radius of tripod 440, barrel length 1,230 diameter 128; eyepiece
length 220, when pushed into barrel it protrudes 84, objective clear aperture 99,
focal length about 1,300, magnification 75 diameters.
The large mahogany tripod stand has a hollow pillar of hexagonal section into which
slides the pillar bearing the telescope mounting. The latter pillar is also of hexagonal
section, and its position may be fixed by a wooden screw On top it carries a
spherical head in two parts, the lower with a circular brass rack, and the upper a
brass knurled knob working a steel worm screw. This provides the azimuth adjustment.
Above this, a short, hexagonal section, brass pillar carries the compass joint pivot
with an altitude adjusting quadrant. This is not calibrated, and is moved by a steel
worm-screw turned by a brass knob. Two butterfly screws fix the barrel of the
telescope to the quadrant.
The round barrel is made of thin wood, probably walnut, stained and polished.
The inside is blackened, and there are three apertures. At each end are brass mounts,
and on top are the two brackets that once held the sighting telescope, now missing.
The objective is composed of two lenses, double convex and concavo-convex, with
an air gap between them. The lenses show the presence of cord (inhomogeneity in
refractivity)» The dust cover over the objective has a smaller aperture, diameter 65.
The draw-tube containing the eyepiece system, is in four sections of length (from
eye end) 22, 62, 50 and 80. The first section has a plano-convex eye lens and a double
convex lens, with a cross-wire between them. The next two sections each have a planoconvex
lens. The eye cap has a deep red glass shade.
The telescope is obviously lot 392, and the stand lot 393 in the Ebeling sale of
June 1791. The catalogue reoftrds that the mahogany stand was made by Kampman,
while the alt-azimuth mounting was by Steitz.
Ebeling (1789,) 75T; Rooseboom (1940b); Engberts (1970) 5:7, an exactly similar stand.
Inv. 7oJ‘2 (
265 BINOCULAR TELESCOPE 1789 (353) Fig. 228, 229
By Jan and Harmanus van Deijl, Amsterdam
Signed on the imtB-ocular adjusting bar: Jan van deyl En Z oon Invr. Fecit
Amsterdam A° 1783
Height to pivot 460, length of binocular tubes 1,010, width of inter-ocular adjusting
bar 115; magnification 56 diameters.
The supporting pillar, with fixed tripod, is attached to the telescope bracket by two
knurled nuts. Altitude adjustment is by a joint with hand tightening knob. The two
telescope barrels are mounted on a stout brass bracket, the right hand one fixed
and the left hand one in lateral slots. The inter-ocular distance is adjusted by two
screwed rods; that between the barrels moves the front of the telescopes, while that
at the end of the bracket moves the eyepiece end. The objectives are achromatic.
The novelty, and rarity, of binocular telescopes seems to have determined Van
Marum to acquire one for the museum. On 25 March, 1791, the Directors allowed
him to bid up to /' 420 for a binocular telescope that was to come up for sale on
the first day of an auction, possibly the Dollond instrument in the Ebeling sale, June
I79I> 391 • Tfiis bought, however, because the Directors’ minutes for
26 October, 179.2, give a detailed reason for getting hold of a Van Deijl instrument.
Van Marum was allowed to buy from Van den Ende, for the sum of ƒ 525, a
binocular telescope constructed by Van Deijl, this being the same as the price
paid by Van den Ende. But over and above this there would be the cost of a chest.
Van den Ende had helped Van Deijl in the construction, and Van Marum wanted
to buy this telescope since another would not be made because of the lack of the
right sort of glass. Payment 0^557-15-0 was made in 1792. The Utrecht University
Museum has aKgh-mounted binocular telescope made by Dollond of London.
Rooseboom (1940b); Bedin||i97i )wfbr some early binocular telescopes.
Inv. 70I4