Abstract
WITH reference to the fine group of sun-spots to which Prof. Piazzi Smyth draws attention in NATURE, vol. xx. p. 602, it may be interesting to mention that the incipient stage of the group in question is shown on two photographs of the sun taken at the Royal Observatory, Greenwich, on October 16 (two days before the date of Prof. Piazzi Smyth's observation). At that time the group consisted of three “veiled” spots and several very small specks hardly to be distinguished from the ordinary pores, together with small faculæ. No photographs were obtained on the next day, and on October 18 enormous changes had taken place, the “veiled” spots having developed into fine sun-spots, with nucleus and penumbra. Four photographs taken on this day show that changes were still taking place, and these continued throughout the remainder of the period of visibility of the group, viz., till October 21, when it passed off at the west limb, No trace of the group is to be found on two photographs taken on October 15, so that it would appear to have formed between October 15 and 16, and must have been quite in its infancy when first photographed on October 16, being then very nearly on the central meridian.
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CHRISTIE, W. Sun-Spots in Earnest. Nature 20, 625 (1879). https://doi.org/10.1038/020625a0
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DOI: https://doi.org/10.1038/020625a0
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