Mr. Henry Pratt has also kindly handed me for use his notes of the Lunar eclipse of August 23, 1877, as seen at Brighton on a splendid night. They were made as the phenomenon progressed, are 58 in number, and in many instances only a few minutes, or even seconds, apart. A selection of them is here given:—9h 13m 50s, first contact of shadow. 9h 30m, shadow very dark; no details of disk easily seen. 9h 40m, first appearance of red. 9h 50m, red all over disk, except margin bluish and S. part green tint. 10h 2m, a sudden brightening of whole disk, in strong contrast to two minutes previously. 10h 15m, E. limb much darker. 10h 35m, south pole decidedly brightest. 10h 44m, S.E. limb much brighter. 10h 48m, whole disk much darker. 10h 51m, S.E. limb brightening again. 11h 1m, N.E. limb brightening. 11h 3m, N.E. limb has darkened and brightened three times during last two minutes. 11h 20m, N. pole has darkened. 11h 21m, N. pole has brightened. 11h 24m 30s, N. pole darker red. 11h 35m, N. pole bright. 11h 35m 30s, same dark and red. 11h 42m, N.E. limb especially bright for a few seconds, and then reddened and shaded again. 11h 49m, S. pole reddened. 12h 1m, S.W. limb reddest part; S. pole red; N. pole paler red. 12h 3m 50s, first appearance of E. limb (my first sketch was made shortly after this, and my second about ten minutes later). 12h 21m, a bright patch on N.N.W. separated from N. pole. 12h 24m, S.W. region is reddest part of eclipse. 12h 40m, redness of shadow fading out.
With a small Browning star-spectroscope Mr. Pratt saw the red and blue ends of the spectrum cut off, but nothing else. Mr. Pratt adds that the red colour was not an effect of contrast or an optical delusion in any way, as was proved by using at times a limited field containing only the red portion under examination. In reference to the curious brightening and darkening of the disk, and the change from time to time of local colour, he says that with much experience he has seen nothing of the same marked character on other occasions, and that “the whole matter was at the time astonishing to me, but none the less real.” The local red patches seen by me seem also to have been observed by Mr. Pratt.
Mr. Pratt’s observation on the floor of Plato.
As an addition to the instances of Tycho, Picard, &c., mentioned in the note on p. 73, Mr. Pratt has also sent me his notes of some observations by him, of “local obscuration of the floor of Plato.” As somewhat condensed, they are as follows:—1872, July 16. While in other parts of the floor spots and streaks were well visible, “the N.W. portion was in such a hazy condition that nothing could be defined upon it.” 1873, Nov. 1. 27 light streaks seen (7 new): the brightness of the streaks was in excess of their usual character, as compared with the craterlets; “an obliteration or invisibility of all the light streaks in the neighbourhood of craterlet no. 1 was very noticeable;” and also “a similar obliteration of the N. end of the streak called the Sector, near craterlet 3.” 1874, January 1. 18 light streaks seen, including 3 new, “some of which outshone other longer known ones. This was curious; for had they been as bright within the last two years as on this occasion I must have noticed them.” Mr. Pratt points out, as worthy of remark, that some months previous to November 1st, 1873, neither craterlets nor streaks on the floor of Plato “had maintained their previous characteristic brightness,”—a fact which he thinks ought to be considered together with the outbreak of brilliancy of both orders on that day, as well as the apparently sudden existence of new ones.
Observation by Mr. Hirst of a dark shade on the moon.
The ‘Observatory,’ March 1, 1879, p. 375, contains an account, by Mr. H. C. Russell, of some Astronomical Experiments made on the Blue Mountains, near Sydney, N. S. W. Among these it is noticed that on 21st October, 1878, at 9 A.M., when looking at the moon, Mr. Hirst found that a large part of it was covered with a dark shade, quite as dark as the shadow of the earth during an eclipse of the moon. Its outline was generally circular, and fainter near the edges. Conspicuous bright lunar objects could be seen through it; but it quite obliterated the view of about half the moon’s terminator, while those parts of the terminator not in the shadow were distinctly seen.
No change in the position of the shade could be detected after three hours’ watching. The observation is made, “One could hardly resist the conviction that it was a shadow; yet it could not be the shadow of any known body. If produced by a comet, it must be one of more than ordinary density, although dark bodies have been seen crossing the sun which were doubtless comets.” The diameter of the shadow from the part of it seen on the moon was estimated at about three quarters that of the moon[11].