sino:= (N E-1Yo) tanO, where 0: is the angle between the normal to the ... 72, 1001 (1958). 2 Optovac, Inc., North Brookfield, Massachusetts, supplied a large.
Erratum: Apparatus for Measuring Magnetothermodynamic Properties to High Fields at Low Temperatures W. F. Giauque, E. W. Hornung, R. A. Fisher, G. E. Brodale, and R. A. Butera Citation: Rev. Sci. Instrum. 35, 1376 (1964); doi: 10.1063/1.1718764 View online: http://dx.doi.org/10.1063/1.1718764 View Table of Contents: http://rsi.aip.org/resource/1/RSINAK/v35/i10 Published by the AIP Publishing LLC.
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found that it would be possible to make such a polarizer. I thank Dr. Robert F. Stewart for helpful discussions.
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FIG. 1. Optical properties of magnesium fluoride, (a) is the vertically polarized component; (b) is the horizontally polarized component. Maximum transmittance for each component is 50%. Accuracy is ±3% transmittance units. Curve (c) is the birefringence.
Rochon type. The idea of making such a polarizer is not new, but until recently, optical quality magnesium fluoride has not been commercially available. 2 Rochon prisms have the advantage of leaving one of the polarized components undeviated. However, we chose the Wollaston design3 because it gives twice the separation of components for the same thickness of material. This separation can be calculated from the relation4 sino:= (N E-1Y o) tanO, where 0: is the angle between the normal to the prism and the ray of the emergent component, 0 is the prism angle, and N E-.Y 0 is the birefringence. We have designed a polarizer· which has a cross section 6X20 mm. It is 3 mm thick with a prism angle (0= arc tan!) of 26.6°. Two matched prisms with optic axes crossed were "air spaced" about 1 mm. This polarizer separates the components at an angle (20:) of 1.12° in the wavelength region 2100 to 1400 A. The optics of our 1-m-grating, normal-incidence, vacuum spectrograph 6 are such that placing the polizer between the slit and the grating, 12.5 cm from the slit, leads to a separation of about 2.45 mm on the photographic plate (Fig. 2). Figure 1 shows the transmittance of the polarizer. We regard it as excellent to 1400 A and usable to 1200 A where the two beams cross. The transmission cut off is about 1125 A. It should be noted that magnesium fluoride may be useful for constructing polarizers for infrared radiation.l The author is indebted to Dr. Richard C. Nelson and Dr. William T. Simpson who, through previous research,
* This research was supported by the Kational Science Foundation under grant No. GP-1918. t National Science Foundation Graduate Fellow. 1 A. Duncanson and R. W. H. Stevenson, Proc. Phys. Soc. (London) 72, 1001 (1958). 2 Optovac, Inc., North Brookfield, Massachusetts, supplied a large optically perfect crystal from which the polarizer was made. 3 See, for instance, Robert W. Ditchburn, Light (Blackie & Sons Ltd., London, 1952), p. 355. 4 M. E. Mascart, Trait D'Oplique (Gauthier-Villars, Paris, 1891), Vol. 1, p. 623. 5 Karl Lambrecht, 3959 N. Lincoln Avenue, Chicago 13, Illinois, fabricated the polarizer. 6 W. Albert Noyes, Jr., A. F. B. Duncan, and Winston M. Manning, J. Chem. Phys. 2,721 (1934).
Letters to the Editor Prompt publication of brief reports of N liW ideas in measurement and instrumentation or comments on papers appearing in this Journal may be secured by addressing them to this department. No proof will be sent 10 the authors. Communications should not exceed 500 words in length. The Board of Editors does not hold itself responsible for tile opinions expressed by tiJe correspondents.
Erratum: Apparatus for Measuring Magnetothermodynamic Properties to High Fields at Low Temperatures [Rev. Sci. Instr. 35, 213 (1964)J
w.
F.
GIAUQUE, G.
E.
E. \V.
HORNUNG,
BRODALE, AND
R. A.
R. A.
FISHER,
BUTERA
Department of Chemistry, University of California, Berkeley, California (Received 23 June 1964)
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HERE is a typographical error in Eq. (6), which should read:
Erratum: Simple Electron Diffraction Camera for the Examination of Alkali Antimonide Photoelectric Films [Rev. Sci. Instr. 35, 508 (1964) J
W. H.
MCCARROLL AND
R. E.
SIMON
Conversion Devices Laboratory, J~lectronic Components and Del'ices, RCA Laboratories, Princeton, New Jersey (Received 22 June 1964) 1200
1400
1600
1800
2000
A(A)
FIG. 2. Spectrum of Lyman source with and without polarizer.
THE
set of photographs in Fig. 2 should be rotated 180° in order for it to agree with the designations given in the figure caption.
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