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Constant Deviation Wavelength Spectroscope


This is a spectroscope coated in a mottled grey-green paint with the collimator and eyepiece set at right angles to one another. The spectroscope sits on a metal base consisting of one foot affixed to an arched section into which a roughly rectangular rail could be inserted; no rail is present. There are two round holes in the top of this. One pillar supports the instrument.

The spectroscope has a metal body and consists of two tubes at right angles to one another, joining at a box. This box can be lifted off to reveal a four-sided prism sitting on a platform. The prism is fixed in place by a bracket and a screw. The platform is connected via an arm to a mechanism that emerges from the box. A metal rotating drum cut with a spiral indentation around its length which is labelled with decimal numbers from 0.9 to 0.39, can be turned to press against this arm and slightly adjust the platform on which the prism sits. A small metal strip engraved with an arrow and attached to a needle underneath runs in the drum as an indicator.

The eyepiece tube emerges from the prism casing with an arched section sitting on a support arm with an adjustment knob underneath. On top of this, there is a round opening covered in a window, behind which is visible part of a scale with a red indicator line on the window glass. This arched section ends in a short section of tubing with a screw tightener on the top. Into this is inserted a plastic tube with a metal end with the eyepiece lens at the other end. The other tube, the collimator tube, also emerges from the prism casing as an arched section sitting on top of a support arm; this converts directly into a tube. Underneath the arched section, there is an adjustment knob. At the end of this, there is a disk-shaped black section with a hole in the end. Just inside of this there are two metal plates next to one another creating a narrow slit. Supported over the slit with a series of narrow metal rods there is a small right-angled prism. Just above the slit opening, there is a small knurled knob, and just below it a round opening with numbers visible inside. Sitting vertically on the top of the disk there is knob with a knurled end and a scale around the rim, and next to this a small adjustment arm.

Accession Number:

Alternative Name:

Spectrograph, Spectrometer, Spectroscope

Primary Materials: Metal: Iron Alloy, Plastic, Glass.


On a plate fixed to the side of the prism cover: “HILGER & WATTS

Scratched into the paint surface on the prism cover and base of the instrument: “1216”

Just above the small knurled knob at the collimator/slit: “1 DIV. = .005 MM.”
Just below the slit: “HILGER”

Dimensions (cm): Height = 39, Width = 44, Length = 48.


This spectroscopy uses a prism to split light into its spectrum of constituent colours for direct viewing or photography. This can be analyzed for numerous purposes, including the chemical makeup of materials or light produced or reflected by materials. A manual for the instrument (<a href=>reproduced here</a>) lists that “together with appropriate accessories” the spectroscope can be used for the analysis of Raman spectroscopy, absorption spectrophotometry, spectrometry in the infrared monochromatic radiation in the ultraviolet, and measurement of wavelength.

This instrument was very likely used in conjunction with a Thin Film Measuring Interference Microscope ( for determining the thickness of a thin material by measuring the difference in optical path length by directing reflected light through the spectroscope.


Excellent: The surface of the instrument is in very good condition, with some marks on the base where the paint has been chipped off or damaged. The paint on the tubes over the instrument is in very good condition, aside from some brown marks on the surface, perhaps residue from tape. The rotating drum is in very good condition, although the knurled knob is dirty. The main prism is present and fully intact, as is the prism suspended in front of the collimator slit. The rods holding this smaller prism in place are rusted all over.

Associated Instruments:

Manufacturer: Hilger & Watts Ltd., England

Date of Manufacture: c. 1948-1968


This item was collected by Erich Weidenhammer in September 2019 from the Second Year Lab (rm 221) at the Department of Physics in the McLennan Physical Laboratories building. It was collected alongside related instrument, which was likely used in conjunction with.

Additional Information and References:

Harvard University’s Collection of Scientific Instruments contains an example of <a href=>this spectrocope</a> as integrated with a thin-film measuring interference microscope via an accessory rail. [17/09/19]

Historical Notes: