Errors of the Computed Times of Solar Eclipse Phenomena


THE final reports of two of the observers of the total solar eclipse of April 28, 1911, have recently been published, giving detailed accounts of their experiences at Vavau, Tonga Islands. Father Cortie's report appears in Proceedings, R.S., No. A595; that of Dr. W. J. S. Lockyer in a publication of the Solar Physics Committee. In reading these reports I have been much struck by the circumstance that both writers appear to have been taken aback by the (to them) unexpected effect of the errors of the lunar tables on the computed times of the various phases of the eclipse. But I wish to point out that they were not left without warning. In Monthly Notices, R.A.S., vol. lxix., p. 31, I stated that with the existing errors of the lunar tables the times of the contacts in this eclipse as there given would be several seconds too late. And as a means of estimating the true times I gave the intervals from the instant when the cusps subtended an angle of specified value at the sun's centre to the commencement of totality. The shift of the moon's actual position relatively to its tabular place would, of course, alter the predicted duration of the eclipse. At the time of publication of my paper (November, 1908), it was not possible to give definite information as to the magnitude of the errors in question, as Newcomb's latest corrections were not then available. But, so far as appears from these reports, the intending observers did not make any further inquiries on the subject before proceeding to draw up their definite programmes of observation. In the circumstances this, surely, would have been a wise precaution.

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