Word: instrument
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Dates: during 1900-1909
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...contrivance for allowing the light to shine through a small hole to the plate. A secondary and more convenient standard will be formed by using a lens in connection with the other apparatus. This will give a light one hundred times as bright as that in the simpler instrument. By means of this same device, the relative brightness of the different stars and planets will also be obtained. The visular comparative brilliancy has already been well ascertained by astronomers, but their comparative brightness for photographic work is not accurately known...
...instrument used in making the observations will be a compound one, so that many negatives may be taken at one time, and will be kept turning to face the sun by means of clock-work...