OBSERVATIONS OF LUNAR OBJECTS. 93 



should be directed. Of the remainder, three have been observed orn^e only 

 by Mr. Gledhill, viz. Wos. 26, 28, and 3-5 ; two have been observed twice, 

 viz. Nos. 27 and 33 ; two thrice, both old spots, viz. 8 (Gruithuisen) and 15 

 (Dawes); and one, 1^0.34, six times between January 15 and March 13, 1870*. 

 In his letter dated 1870, May 19, Mr. Pratt says that " spot No. 8 could 

 not be recovered even with the most minute attention." Of spot No. 1 he 

 says, " it was brighter than I have seen it before, quite round and dense, 

 much hke the image of a star on a good night surrounded by the very least 

 trace of a ring of light. [Neither] internal nor external shadows could be 

 seen, although I constantly expected a slight glimpse." 



Spot No. 22. 



In reference to this spot Mr. Pratt writes, under date 1870 August 2Q, as 

 follows : — 



" Spot No. 22, according to my observations, has manifested a remarkable 

 increase of brightness, and those parts of the shaded portions of the floor of 

 Plato which are nearest to the rim have come out more conspicuously darker 

 than the rest than I remember to have previously noted. The tint of the 

 floor, too, has progressively paled. These three phenomena [the increased 

 brightness of spot 22, the intensification of the darker parts of the floor near 

 the rim, and the progressive paling of the floor] may possibly be connected 

 by a common cause ; for certainly in this lunation there is somewhat of a 

 coincidence amongst them ; for instance, spot 22 is intensely bright at the 

 time the marginal portions of the shaded parts are most conspicuously dark, 

 and these two, again, coincide with the time when the general tint of the 

 floor is at its darkest. Again, after August 12 and 13, spot 22 decreased in 

 relative intensity, although I am not ready to hazard the assertion that it 

 had on August 16 positively declined to its \isual intensity, as it was not 

 seen. [It was on this evening that Mr. Pratt observed three spots only.] 

 Two similar instances, I believe, I have noted before, when 22 manifested a 

 singular brightness at sunrise. But the connexion between the visibility of 

 the deeper-tinted margin and the general deepening of colour is perhaps more 

 close still, as both certainly paled after August 13. The perplexity seems to 

 be that the variation in intensity of the margin is relative in respect of the 

 general colour ; and if difiorences of angles of illumination and vision do affect 

 the general tint, it might be supposed that they would in the same manner 

 afi'ect the margin and so produce no relative variation of intensity." 



In connexion with the relative intensity of which Mr. Pratt speaks, the 

 state of the border is somewhat important. August 12 and 13, when the 

 marginal portions of the floor were intensified in colour, Mr. Pratt recorded 

 of the border : — " Definition fair at times, with much tremor, wind N.E." 

 This was on the 12th. On the 13th the record is : " Border, definition bad, 



* The history of spot No. 34 is curious ; the following are the only records which exist 

 of it. The observations were all made by Mr. Gledhill with the Halifax 9 J-inch equatorial 

 in the Observatory of Edward Crossley, Esq. 



1870, January 15, 10 to 13 hours. " I am continually thinking I see an object close to 

 No. 1 and to the west of it." 



February 11, 6.45. " No. 1 often comes out double ; last year I often saw it thus. I am 

 now almost quite sure I see a minute object close to the west of it." 



February 12, 6.0. " Saw 9, 11, 30, and object close west of No. 1." 



March 12, 6 to 8 hours. No. 34 mentioned as having been seen. 



March 13, G to 12 hours. "Unless I am very much mistaken indeed 34 is an easy 

 object, i. e. No. 1 comes out easily double." 



There are no records after this date. Instruments less than 9-inches aperture are not 

 likely to redetect it. 



