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1870, September 9. Mr. Elger recorded No. 5 faint, 17 especially faint, 14 and 22 glimpsed, and 14 difficult.

Interval 168 hours to Meridian Passage.

1870, June 13. Mr. Gledhill has this remark: "For some time I have thought that when power 115 was used, spot No. 4 was almost at any time to be seen, or at any rate a condensation of the sector' at its apex was seen. On applying 240, however, the appearance vanishes, and no condensation or spot is seen, or perhaps only sometimes and at intervals."

Interval Meridian Passage to 168 hours.

1870, July 13. Mr. Gledhill records No. 1 as very bright.

1870, September 10. Mr. Elger records Nos. 25 and 16 as easy, No. 14 as seen by glimpses.

Interval 168 to 156 hours.

1870, August 12. Mr. Neison records "a spot seen on the border of No. 3, very small and hardly visible except at intervals, but pretty bright on edge only of the light marking." Mr. Neison suspected it to be No. 31, which it undoubtedly is according to the position which he has accorded to it on the diagram. Mr. Neison was the only observer who detected No. 31 during this lunation, on the 10th and 11th of August, as an elongation of No. 3. Mr. Elger, Mr. Gledhill, and Mr. Pratt appear to have missed it. Query, was the group Nos. 3, 30, and 31 in greater activity about this time? Mr. Neison has this note, "3. Faint indications of its being a crater very distinct." Mr. Pratt records: "During the long period since I last saw the light streaks I have had little opportunity to study former sketches, and so was free in a measure of the bias of them. Yet on sketching those seen, the forms, positions, and directions coincide with former drawings, notably the trident a, 6, n, l." Mr. Pratt also notices a remarkable increase in brightness of spot No. 22, so as to attract especial attention. Neither Messrs. Elger, Neison, Ormesher, nor Gledhill noticed this spot, although they were observing on the same evening as Mr. Pratt, who further remarks "that in moments of best definition the area comprised between Nos. 19, 1, and 4 was not nearly so well displayed as the rest of the floor, giving a strong impression of an obscuring medium located there." [This observation of the streak 1, the existence of which has been questioned, is perfectly independent of any suspicion of its non-existence, as it occurred some months before the question was raised.]

1870, October 10. Mr. Elger found spot No. 5 on the E. edge of the E. arm of the "trident;" its position, as given by Mr. Pratt, is on the W. edge of the E. arm. He also found that Nos. 5 and 14 were far inferior to 17. Spot No. 25 was easy. Mr. Elger did not see spots Nos. 9, 11, 18, 23, nor 30 recorded by Mr. Gledhill, nor did Mr. Gledhill see No. 14. For a special note on the position of spot No. 5, which Mr. Elger also saw on the E. edge of the "trident" on May 13, 1870, see Interval 132 to 144 hours. 1870. On the 12th of August, and on September 7, 11, and 12, Mr. Neison made a series of observations with apertures varying from 4 to 51 inches, with differences of of an inch.

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Inches Spots The spots seen were Nos. 1, 3, 4, and 17 with 4 and 44 inch apertures, the same and No. 5 with 44 and 44; with 5 inches aperture spot No. 14 was detected and marked as faint, and with 54 inches No. 16 was discerned:

the last two, Nos. 14 and 16, were in all cases marked as "faint," sometimes extremely so.

These seven spots are precisely those which have the highest degrees of visibility for 18 lunations, as under :

Spots ...

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Visibility . 1.000 897 ·887 830 510 433 294 From these observations, it appears that spots Nos. 1, 3, 4, and 17 may be detected with instruments between 4 and 44 inches of aperture, that spot No. 5 requires an extra half inch, or 4 to 5, and that 5 and 51 will bring out spots No. 14 (5 inches) and 16 (5 inches).

Aperture, of course, is an important element of visibility; and as these spots are seen with apertures under six inches, as the observations increase, and the normal degrees of visibility become well determined, variations in the visibility of these spots may be detected with instruments of 6 inches aperture, provided the observations extend over a sufficiently long period.

Elements of Visibility.

Lunar.-Brightness and size of spots.

Terrestrial. Clearness and steadiness of atmosphere.

Instrumental.-Goodness of figure of object-glass or mirror, and extent

of aperture.

Physiological.-Keenness of eyesight.

Interval 156 to 144 hours.

1870, July 14. Mr. Gledhill records No. 1 as a fine, large, bright spot, No. 17 as a small bright spot, Nos. 3 and 30 as bright spots, and No. 5 a bright spot, seen now and then. Mr. Ingall records No. 1 as very plain and sharp, No. 4 as steadily seen, and Nos. 3, 31, 30 a misty spot, probably consisting of these three.

1869, August 23. Mr. Pratt records that "spots Nos. 1, 3, 4, 17, 6, and 14 were very bright compared with their usual appearance, and all easily seen. No. 4 was not well defined; there was a persistent oval light round it (N.W. and S.E), and I several times believed it to be double, but could not be positive it was so. So remarkably clear was the vision that several times as many as four or five spots were held in view at once, without looking directly for them, and two or three times as many as six were so seen, viz. Nos. 1, 3, 4, 17, 5, and 14; again, Nos. 1, 3, 4, 17, 6, and 5. Nos. 4, 7, 6, 17 were a group seen together, and Nos. 5, 14, 22, and 1 were a similar one; yet still so exceedingly delicate are the fainter spots and the fainter traces of light on the floor that it needs a most concentrated attention to see either. In looking for the faint spots the faint traces of light will escape notice; again, when looking for the latter, the former are most likely not to be seen. This exceeding delicacy too interposes a serious difficulty in aligning them with objects on or near the border: the eye cannot hold so wide a view and at the same time retain a sufficiently correct impression of objects at once so faint and small. These remarks do not apply to the easier spots and light streaks. Once, for a few minutes, a narrow, dark, straight line, like a pencil-mark, was visible from m towards Rambleta [i. e. from N.W. to S.E.], probably the crack Mr. Birt has discovered. It was not seen again this evening."

1870, September 11. Mr. Neison records No. 1 as very distinct, No. 3 as distinct and brilliant, Nos. 5 and 14 as faint, 5 as rather so.

Interval 144 to 132 hours.

1871, March 8. Mr. Ormesher records a spot near the S.W. border, which he queries "14, a long way off" from its position. Is it a spot not before recorded?

1870, August 13. Mr. Gledhill records spots Nos. 3 and 17 as fine bright disks, No. 1 as a fine, large, bright disk, and No. 4 as a nebulous object. Mr. Pratt remarks that "on this evening, as well as in 1870, August 12, the tint of the dark portions of the floor was much intensified close to the rim. It was the case all round, but especially so between 6 and 4, between e and , and between ß and n."

1869, December 20. Mr. Pratt places a spot nearly due north of No. 1 on the diagram of this evening, which he queries as 23. I query it as uncertain. Spots Nos. 1, 0, 23, and 16 very nearly align. The line passing through Nos. 1, 0, and 23 passes slightly west of No. 16. Mr. Pratt's spot is very decidedly east of this line. [1871, March 31. The spot registered by Mr. Pratt on Dec. 20, 1869, not having been reobserved, it is probable that it may have been, as Mr. Pratt queried, No. 23. I have now entered it as such.-W. R. B.]

Interval 132 to 120 hours.

1870, September 12. Mr. Neison records of No. 22, "a spot very faint, and difficult to make out in the midst of a patch of light.”

Interval 108 to 96 hours.

1870, July 16. Mr. Gledhill records spot No. 1 as "a fine, large, bright disk; looks like an elevation;" also Nos. 3 and 17 as bright disks. I have made the following note on the Form :-"9 and 0. These do not appear in their precise localities, especially 0. It may be that the spot thus marked by Mr. Gledhill is a new one."

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1870, December 12. Mr. Pratt writes: "A faint crepuscular kind of shade has crept over the western part of the floor, and is deepest near the western border; but the gradation is very delicate, 12 hours to 12 hours 40 minutes." [1870, March 24. Mr. Gledhill noticed a darker tint at the west part of the floor, and furnished a tinted sketch: see remarks under this date (p. 87); also Mr. Elger's observations of the same portion of the floor being light, under date 1870, August 6, interval 48 to 60 hours.]

1870, November 11. Mr. Gledhill records spots Nos. 1, 3, 30, and 17 as bright spots. On the 13 of September (same interval) he recorded them as "bright or fine craters;" with the exception of Mr. Neison's record on August 12 of No. 3 as a suspected crater (interval 168 to 156 hours), this interval (108 to 96 hours) is the earliest in the declining day that the four have been seen as craters. The terminator is recorded as west of Fracastorius. 1870, September 13. Mr. Gledhill records spots Nos. 1, 17, and 30 as bright or fine craters, and says of 17, "fine crater as 1 and 3;" but of 3 he says, "fine disk." I have marked 3 as a crater.

Interval 96 to 84 hours.

1870, August 15. Mr. Pratt records that the darker margins of the shaded parts of the floor are still visible as on the 12th and 13th August, but not in such striking contrast.

1870, October 13. Mr. Pratt records spot No. 1 as brilliant, the others dimmer than usual.

Interval 84 to 72 hours.

1869, August 26. Mr. Pratt remarked a decided difference in definition

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the last two, Nos. 14 and 16, were in all cases marked as faint," sometimes extremely so.

These seven spots are precisely those which have the highest degrees of visibility for 18 lunations, as under :

Spots ......

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Visibility.. 1.000 .897 •887 830 510 433 294 From these observations, it appears that spots Nos. 1, 3, 4, and 17 may be detected with instruments between 4 and 44 inches of aperture, that spot No. 5 requires an extra half inch, or 4 to 5, and that 5 and 51 will bring out spots No. 14 (5 inches) and 16 (5 inches).

Aperture, of course, is an important element of visibility; and as these spots are seen with apertures under six inches, as the observations increase, and the normal degrees of visibility become well determined, variations in the visibility of these spots may be detected with instruments of 6 inches aperture, provided the observations extend over a sufficiently long period.

Elements of Visibility.

Lunar.-Brightness and size of spots.

Terrestrial. Clearness and steadiness of atmosphere.

Instrumental.-Goodness of figure of object-glass or mirror, and extent

of aperture.

Physiological.-Keenness of eyesight.

Interval 156 to 144 hours.

1870, July 14. Mr. Gledhill records No. 1 as a fine, large, bright spot, No. 17 as a small bright spot, Nos. 3 and 30 as bright spots, and No. 5 a bright spot, seen now and then. Mr. Ingall records No. 1 as very plain and sharp, No. 4 as steadily seen, and Nos. 3, 31, 30 a misty spot, probably consisting of these three.

1869, August 23. Mr. Pratt records that "spots Nos. 1, 3, 4, 17, 6, and 14 were very bright compared with their usual appearance, and all easily seen. No. 4 was not well defined; there was a persistent oval light round it (N.W. and S.E), and I several times believed it to be double, but could not be positive it was so. So remarkably clear was the vision that several times as many as four or five spots were held in view at once, without looking directly for them, and two or three times as many as six were so seen, viz. Nos. 1, 3, 4, 17, 5, and 14; again, Nos. 1, 3, 4, 17, 6, and 5. Nos. 4, 7, 6, 17 were a group seen together, and Nos. 5, 14, 22, and 1 were a similar one; yet still so exceedingly delicate are the fainter spots and the fainter traces of light on the floor that it needs a most concentrated attention to see either. In looking for the faint spots the faint traces of light will escape notice; again, when looking for the latter, the former are most likely not to be seen. This exceeding delicacy too interposes a serious difficulty in aligning them with objects on or near the border: the eye cannot hold so wide a view and at the same time retain a sufficiently correct impression of objects at once so faint and small. These remarks do not apply to the easier spots and light streaks. Once, for a few minutes, a narrow, dark, straight line, like a pencil-mark, was visible from m towards Rambleta [i. e. from N.W. to S.E.], probably the crack Mr. Birt has discovered. It was not seen again this evening."

1870, September 11. Mr. Neison records No. 1 as very distinct, No. 3 as distinct and brilliant, Nos. 5 and 14 as faint, 5 as rather so.

Interval 144 to 132 hours.

1871, March 8. Mr. Ormesher records a spot near the S.W. border, which he queries "14, a long way off" from its position. Is it a spot not

before recorded?

1870, August 13. Mr. Gledhill records spots Nos. 3 and 17 as fine bright disks, No. 1 as a fine, large, bright disk, and No. 4 as a nebulous object. Mr. Pratt remarks that "on this evening, as well as in 1870, August 12, the tint of the dark portions of the floor was much intensified close to the rim. It was the case all round, but especially so between 6 and 5, between e and, and between ẞ and n."

1869, December 20. Mr. Pratt places a spot nearly due north of No. 1 on the diagram of this evening, which he queries as 23. I query it as uncertain. Spots Nos. 1, 0, 23, and 16 very nearly align. The line passing through Nos. 1, 0, and 23 passes slightly west of No. 16. Mr. Pratt's spot is very decidedly east of this line. [1871, March 31. The spot registered by Mr. Pratt on Dec. 20, 1869, not having been reobserved, it is probable that it may have been, as Mr. Pratt queried, No. 23. I have now entered it as such.-W. R. B.]

Interval 132 to 120 hours.

1870, September 12. Mr. Neison records of No. 22, "a spot very faint, and difficult to make out in the midst of a patch of light."

Interval 108 to 96 hours.

1870, July 16. Mr. Gledhill records spot No. 1 as "a fine, large, bright disk; looks like an elevation;" also Nos. 3 and 17 as bright disks. I have made the following note on the Form :- "9 and 0. These do not appear in their precise localities, especially 0. It may be that the spot thus marked by Mr. Gledhill is a new one."

1870, December 12. Mr. Pratt writes: "A faint crepuscular kind of shade has crept over the western part of the floor, and is deepest near the western border; but the gradation is very delicate, 12 hours to 12 hours 40 minutes." [1870, March 24. Mr. Gledhill noticed a darker tint at the west part of the floor, and furnished a tinted sketch: see remarks under this date (p. 87); also Mr. Elger's observations of the same portion of the floor being light, under date 1870, August 6, interval 48 to 60 hours.]

1870, November 11. Mr. Gledhill records spots Nos. 1, 3, 30, and 17 as bright spots. On the 13 of September (same interval) he recorded them as "bright or fine craters;" with the exception of Mr. Neison's record on August 12 of No. 3 as a suspected crater (interval 168 to 156 hours), this interval (108 to 96 hours) is the earliest in the declining day that the four have been seen as craters. The terminator is recorded as west of Fracastorius.

1870, September 13. Mr. Gledhill records spots Nos. 1, 17, and 30 as bright or fine craters, and says of 17, "fine crater as 1 and 3;" but of 3 he says, "fine disk." I have marked 3 as a crater.

Interval 96 to 84 hours.

1870, August 15. Mr. Pratt records that the darker margins of the shaded parts of the floor are still visible as on the 12th and 13th August, but not in such striking contrast.

1870, October 13. Mr. Pratt records spot No. 1 as brilliant, the others dimmer than usual.

Interval 84 to 72 hours.

1869, August 26. Mr. Pratt remarked a decided difference in definition

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