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<p>Particulars have been given of some tests on tubes containing helium with a view to their being used as standards of light. It was then found that small differences in thickness in the bore of the capillary tubes used introduced errors and more uniform tubes, which were also fairly free from striations, have since been obtained. Details of the photometric tests to which these tubes were subjected are given. The mean deviation in candle-power per cm. length of tube is found to be 1.15 per cent., and the max. deviation in any tube 3 per cent. The chief improvement to be sought in the next series of tubes to be made is complete freedom from striations.
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<br>Subjects: photometry</div>
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Nutting, P.G.</div>
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