Errors of the Computed Times of Solar Eclipse Phenomena


WITH regard to Dr. Downing's remarks, I was aware from his published statement that the predicted time of totality would probably be several seconds too late, but little thought that the error would amount to so much as twenty seconds of time. The precaution was naturally taken to observe closely the diminishing cusp and to arrange to give the necessary time signals from the cusp data mentioned by Dr. Downing in the above letter. Unfortunately, however, while the cusp was visible nearly up to second contact, the image of it on the screen had been oscillating so violently (due to air tremors) that the officer in charge had previously decided to give the necessary signals at the computed times from the chronometer. (See page 17 of my report for details of the actual procedure.) It is true that no inquiry was made by me to find out what error might be expected, but it was assumed that if such a large error had been approximately known it would have been published. It would be advantageous if the present director of the Nautical Almanac could find his way to make generally known the approximate values of such errors a short time previous to the setting out of eclipse expeditions.

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