Hilger & Watts Spectrometer D 186.3/290

© Brooke Clarke 2014

Hilger & Watts Wavelength Spectrometer

    Accessories & Applications



This was called a "Wavelength Spectrometer" and appears to be a modular, i.e. universal instrument that could be configured to do many different things.

Reading while waiting for it to arrive.  If you have any documentation (ads, catalogs, data sheet, manual, report with data from, &Etc.) on these please let me know.
Photo of another of these, not mine.
Hilger & Watts Spectrometer

Recently I've been interested in prisms and the generation of a rainbow of colors (Wiki: Prism, Dispersive prism, Minimum deviation, Abbe prism, Littrow prism, Littrow Angle, Pellin–Broca prism, Amici (not roof) prism, Compound prism, Abbe number).

A dispersive prism bends the incoming light into a rainbow (Wiki: spectral dispersion).  This is different than deflection prisms (Wiki) in that a deflecting prism does (should) not separate the colors, but just bend or reflect the light.

Spectrophotometer (Wiki) measures light intensity (or polarization) at some specific wavelength.  Ideally the rainbow spectrum would be spread a great deal so that absorption lines can bee seen.  This allows identifying chemical elements by their lines, called Spectroscopic analysis (Wiki).  Spectroscopic analysis allows measuring the concentration of a specific element, like in the Spectronic 20D Spectrophotometer where a rotating grating is used to select a specific wavelength of light that passed through a liquid sample and the intensity is measured.  Typically there's a Monochromator (Wiki) prior to the sample so that only a narrow bandwidth of light strikes the sample.  It seems to be that it would be better to add a way to look at the wavelength of light coming from the sample.  That way florescence (Wiki) could be quantified.

Another application is in Astronomical spectroscopy (Wiki) which can be used to derive many properties of distant stars and galaxies, such as their chemical composition, temperature, density, mass, distance, luminosity, and relative motion.  A Spectrohelioscope (Wiki) allows analyzing many aspects of the Sun.  A Heliostat (Wiki) is a device that tracks the Sun.  For example a heliostat could be used to send the Sun's image to the Spectrohelioscope.  A Heliotrope (Wiki) is a mirror that acts as a survey target.  This is very similar to the signaling Heliograph (Wiki), for example the Mance Type Mk V Heliograph.

Fraunhofer lines (Wiki) were originally observed as dark features (Wiki: absorption lines) in the optical spectrum (Wiki) of the Sun (Wiki).

Czerny–Turner monochromator (Wiki) is also a way to make a spectrograph with either a grating or prism.

A Diffraction grating (Wiki) can be used in place of a prism to form a rainbow.  Blazing (Wiki) is shaping of the surface to optimize the performance at some wavelength, typically done with a triangular shape rather than a non blazed sine wave.

History of spectroscopy (Wiki).
Atomic emission spectroscopy (Wiki)
Atomic absorption spectroscopy (Wiki)
Absorption spectroscopy (Wiki) Specific Approaches (Wiki)
Lamb shift (Wiki) shows an error in the Dirac equation (Wiki) which led to Quantum electrodynamics (Wiki QED) by Richard Feynman (Wiki) and others.
Multipass spectroscopic absorption cells (Wiki) used for diffuse samples, like air.

Resolution (Wiki- close but not it) is a measure of how narrow a band a given spectrum analyzer displays for a single wavelength signal.
Resolution = (signal wavelength) / (displayed bandwidth)

The lowest resolution (R~1E3) is a single prism, next is a series of prisms, next is a grating (R~) and even higher is the Fabray-Perot spectrum analyzer (Wiki: F-P) (R~1E6).

Beer–Lambert law (Wiki)

Ebay Description

Photo from eBay listing.

Hilger & Watts Spectrometer D 168.3/290 Hilger & Watts Spectrometer D 168.3/290

Manufacture: (Hilger & Watts) Morton Grove, London, about 1963

Function: Used for spectrochemical analysis, absorption, spectrophotometry (Wiki), wavelength measurement, Raman spectrography (Wiki), monochromatic radiation in the UV, and spectrophotometry in the IR, to name but a few of the scientific uses of this instrument.

Description: The spectrometer is mounted on a machined cast iron base with dovetail groves for mounting accessories. A control box is linked to the spectrometer, which has a filar eyepiece. The knob on the control box was used to rotate the spectrometer's prism, since its collimator and telescope are held fixed at all times. There is a precision scale to read the wavelength, with a magnifier for reading the scale. The spectrometer has an adjustable slit with a micrometer adjustment to control the slit width. There is a small transformer with electrical cord terminating in a standard 3-prong AC plug."

I believe this design is a "Littrow Spectrometer" (see Wiki: Littrow Angle) where the light goes through the prism then down the tube and is reflected back to the prism and bent a second time finally leaving the tube.  More on this once I've received it.


It will need to be determined by reverse engineering or if you have ANY documentation on this please let me know.


As Received Box 1 bad packaging.

Fig 1 First Box as received
No packing material, just loose items in bottom of box
Not a good sign
                      & Watts Spectrometer D 168.3/290
Fig 2
Second box contained only the stand
and was packaged OK
Fig 3
Box 3
To be received.

Individual parts as received

Fig 10 Stand
Bottom view.
Bed (Fig 21) fits machined notches and held with 2 bolts (Fig 20).
Hilger & Watts Spectrometer D 168.3/290
Top View
Alignment pins locate condenser, prism & telescope assemblies
with precision

Hilger & Watts Spectrometer D 168.3/290

Fig 11 Accessory Pillar (use?) fits bed (Fig 21)
Hilger & Watts Spectrometer D 168.3/290
Fig 12 Accessory Table (use?)
Hilger & Watts Spectrometer D 168.3/290
Fig 13 X-Y-Tilt Adjustable Table (Fig 12) Support

Hilger & Watts Spectrometer D 168.3/290

Hilger & Watts Spectrometer D 168.3/290
Fig 14  X-Y-Tilt Adjustable Support mounts to post on Table (Fig 12)

Hilger & Watts Spectrometer D 168.3/290

Hilger & Watts Spectrometer D 168.3/290
Fig 15 Prism Cover

Hilger & Watts Spectrometer D 168.3/290

Hilger & Watts Spectrometer D 168.3/290
Fig 16 Pellin–Broca prism & Micrometer Wavelength Drive
Drum Calibrated from 0.38 to 2.0 microns or
380 to 2000 nm.
Drum dia = 1.572" and it takes about 6 turns, so:
Scale length = 6*2 * PI * 1.572" = 59"
calibration ticks at 2 microns are 0.01 microns (10nm)  and at 0.38 the ticks are 0.001 microns (1 nm)

Drum marked EDF 1628

Hilger & Watts Spectrometer D 168.3/290

Hilger & Watts Spectrometer D 168.3/290
Loosening knurled ring at end of drum frees drum allowing setting
wavelength to match known line.

The lower plate holding prism pivots on ball bearing.
The upper plate can be adjusted (opposing screws at right end) relative to lower plate in rotation, why?
Fig 17 Astronomical Telescope
Large knob for focus.
Focus scale under small glass window on top.
Small knob may be for locking focus?
I have it focused on nearby mountain top.
Eyepiece mating dia = 20.32mm (0.800")

Hilger & Watts Spectrometer D 168.3/290

Hilger & Watts Spectrometer D 168.3/290

Cross hairs are in large black cylindrical housing that holds eyepiece.  Rotate it to make hairs horizontal or vertical.
Bring cross hairs to focus by pulling/pushing eyepiece.

Fig 18 Variable Slit & Condenser

Hilger & Watts Spectrometer D 168.3/290

Hilger & Watts Spectrometer D 168.3/290
Micrometer adjusts slit width.
Knurled knob just below "1 Div = .005mm" adjusts slit height, note number "9" that varies with height.
Note sure about why the small prism, maybe to allow light to come from a right angle?

Lever is input shutter.

Hilger & Watts Spectrometer D 168.3/290
Fig 19 Wavelength Drum Illuminator
& Drum Reading Magnifying Glass
Attaches to stand using two small screws (Fig 20).

Hilger & Watts Spectrometer D 168.3/290

Hilger & Watts Spectrometer D 168.3/290

Hilger & Watts Spectrometer D 168.3/290
Wire needs to be soldered to base of socket.
Fig 20 Box 1 hardware
2 bolts attach bed to stand.
2 screws attach Illuminator to stand
1 plate (maybe related to Illuminator?)
Hilger & Watts Spectrometer D 168.3/290
Fig 21 2' long Bed
Held to the stand with two each: 1/2"-16 x 2" bolts (Fig 20)

Hilger & Watts Spectrometer D 168.3/290
Fig 22 Partially Assembled
Input light at upper right (Condenser).
Prism at upper left.
Telescope along left side.
The accessory equipment gets installed on the input at right.

Hilger & Watts Spectrometer D 168.3/290

Accessories & Applications

Most of this information comes from Reference 1.
Note that the direct reading (calibrated drum) wavelength spectrometer shown is the first generation.  The D168.3 unit shown on this web page is a newer model.

Lummer-Gehrcke Parallel Plate

A quartz plate increases the resolving power to about 200,000.

Lummer-Gehrcke Parallel Plate for Hilger
                      Watts Spectrometer

Fabry-Perot Etalon

Used to determine the e/m ratio for the electron using the Zeeman effect.
Fabry-Perot Etalon for Hilger Watts

Nutting Photometer

A very accurate type of photometer.
Nutting Photometer for Hilger Watts


1682572 Optical instrument, Keuffel Carl W, Keuffel & Esser Co, Aug 28, 1928, 356/300, 356/217, 356/232 -
2143160 Spectrometer, Mclachlan Robert W, Slingland Charles E, Jan 10, 1939, 434/303, 359/438 - Teaching demonstration type
2330694 Spectrometer, Estey Roger S, Harper Kennard W, Spencer Lens Company, Sep 28, 1943, 356/300 -hand held Littrow reflecting prism design
2744439 Spectrometer systems to compensate for the wandering of light rays, ill Jr George C, Leeds & Northrup Co, May 8, 1956, 56/307, 250/205
2945953 Grating spectrometers, Martin Albert E, Parsons & Co Sir Howard G, Jul 19, 1960, 356/334, 250/504.00R, 359/351, 356/333


Optical Spectrum Analyzers
Monolight- rotating optical grating
Beseler PM1 Darkroom Color Analyzer - variable color filters in front of photomultiplier tube (Wiki PMT)
Wollensak L3524D Direct Vision Spectroscope - wavelength scale can be calibrated using table salt in a flame.
Ocean Optics HR2000 Spectrometer - coverts 467 nm to 670 nm i.e. uses the H9 grating and a linear CCD sensor, USB interface to computer
Electro-Optical Gadgets
M18 IR Binocular
PAS6 Metascope IR Viewer & IR Source
IR Beacon
M227 Signal Lamp Equipment SE-11
UAS-4 Infrared Surveillance System, AN/AAS-14 Infrared Detecting Set, MK-898/AAS-14A IR Optical Filter Kit
Theodolites -
Leitz 115 Transit -


Specific to the Hilger constant deviation spectroscope

A Spectroscope of Fixed Deviation, Pellin & Broca, Dec 1899, Astrophysical Journal, vol. 10, p.337

The Rotation of Prisms of Constant Deviation (references: 1899 A Spectroscope of Fixed Deviation), Forsythe, May 1917 Astrophysical Journal, vol. 45, p.278 - How to align the center of rotation of the prism on a Hilger spectrometer prism table using diaphragms on telescope and collimator.


Ref 1: Advanced Practical Physics For Students Worsnop & Flint 1927 - free on line pdf version.

The Electron Theory of Matter (1914) by Richardson - free on line pdf version.
Measuring e/m (Wiki) using the Zeman Effect (Wiki)
Has a chapter on the Aether and various experiments that tested the idea.
Ch. 20 Spectroscopic Phenomena

An Introduction to the Theory of Optics (1909) by Schuster - free on line pdf version -
"..the resolving power of prisms depends on the total thickness of glass, and not on the number of prisms, one large prism being as good as several small ones."

From Classical to Modern Chemistry: The Instrumental Revolution  edited by Peter J. T. Morris (2002),
 it has chapter:  Adam Hilger, Ltd. and the Development of Spectrochemical Analysis by Charlotte Bigg.

Practical Hints on Absorption Spectrometry: Ultraviolet and Visible 1966, J. R. Edisbury (Hilger & Watts) (on order in the hope is has something about this spectrometer).

The following selection is from: T. Thorne Baker, The Spectroscope and its Uses in General Analytical Chemistry. William Wood and Co. New York (1923).
Chapter 2 is on line

Taylor Hobson acquired Hilger & Watts in 1969 (Wiki).
Harvard's Collection of Historical Scientific Instruments - constant deviation wavelength spectrometer
The Spectrohelioscope Network - Fred Veio

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Page created 21 Nov 2014