Abstract
IN the interesting account of a solar outburst on July 25 contained in your last number (p. 508), Mr. Hennessey says that “unhappily the sun remained invisible till July 30.” Referring to our sketches of the solar surface, I find that the nearest in time to the date of the outburst are those made on July 21 and 27. On the intervening days clouds prevented all solar work. The sketch on July 21 shows the groups in the [n p] quarter of Mr. Hennessey's disk, and that of July 27 gives those in the [n f] and [s f] portions, and also the two groups in the [n p] which were farthest from the centre on the 21st. There was certainly not the slightest trace on the 21st of the remarkable group which burst forth so suddenly on the 25th, and there can be very little doubt that the spots in the [n p] quarter on the 27th are identically the same as those in the [n f] quarter on the 21st. Drawings of the solar disk are made here on every available day, and the position of each spot is marked with the greatest exactness; but when the sky is cloudy, as on the 27th, it is not always possible to fill in all the details. The exact position of each spot is invariably marked before any details are sketched, and therefore, as the definition on the 27th was good, the group, which suddenly appeared near the centre of the disk on the 25th, must already have completely vanished. I might mention, in conclusion, that our magnetic photograms show no sign of any disturbance synchronous with the solar outburst.
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PERRY, S. The Solar Outburst of July 25, 1881. Nature 24, 556 (1881). https://doi.org/10.1038/024556c0
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DOI: https://doi.org/10.1038/024556c0
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