A variable angle constant deviation prism. A `null' method of measuring curvatures

• Published in: Measurement science & technology 2002-04, Vol.13 (4), p.494-502
• Main Author: Goldsack, S J
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Optical instruments, equipment and techniques; Physics
• ISSN: 0957-0233; 1361-6501
• DOI: 10.1088/0957-0233/13/4/311

This paper describes an instrument for measuring curvatures by a 'null' method. It was originally designed to measure the momentum of tracks in a cloud or bubble chamber operating in a magnetic field. The curvature introduced into an image by projection through a prism is used to straighten the track image, straightness being judged by sighting along the image at a near grazing angle. The curvature required measures that of the image. The original concept was introduced by Blackett in about 1936 and was widely regarded as a very elegant technique, capable of providing measurements at least as accurate as those obtained by more traditional approaches but in a much shorter time. This paper briefly reviews the work of Blackett (which received only the most cursory description at the time). It then continues to describe a development of Blackett's idea intended to stretch its capabilities, particularly towards higher curvatures. This work was carried out in about 1961 but was not described in the literature at the time. At present the work is perhaps of mainly historic interest, but it does seem likely that other uses for the technique may exist now or in the future. (Author)