94 REPORT 1871. 



much boiling, wind N.E." On the 12th, definition fair, the floor was recorded 

 as " very dark." On the 13th it was dark, but not so much so as on the 

 12th. On the 16th, as well as on the 15th, the definition of the border was 

 " bad." These records clearly throw a doubt upon the supposition of the 

 " paling " having resulted from some lunar action, inasmiich as when, the 

 deeper tint was observed the definition was "good," the "tremor" and 

 " boiling " having a tendency to confuse the portions of the floor. On the 

 other hand, spots have been much more numerous with bad definition than 

 3 as observed by Mr. Pratt on the l(3th ; and this would lead to the supposition 

 that the (qrparent extinction of the spots with a pale floor was in some 

 way differently connected than by a deteriorated state of the earth's atmo- 

 sphere. I have often observed that the passage of a thin cloud over the 

 moon has greatly contributed to intensify the tints of the darker portions of 

 the surface ; but in this case the intensification has been general and not 

 partial, as it would be if dependent upon local lunar action. 



Mr. Pratt records a case of parfial obscuration which was well seen oil 

 August 13. " It appeared," says Mr. Pratt, " on this wise. A general view 

 of the floor showed it much speckled and streaked in other pai'ts ; but over 

 the area specified [Mr. Pratt has not mentioned the particidar part of the 

 floor ; but from what follows I apprehend it must be in the neighbourhood of 

 No. 3] there seemed an absence of markings ; close attention, however, 

 enabled some to be seen, but not nearly so richly as the remainder of the 

 floor, and we know well enough that that particular area is not wanting in 

 markings. The evening's view has just occurred to memory when I first 

 discovered that spot 3 was a triple one, and had a remarkalile view of its 

 neighbourhood [Qy. "Was this on May 13 ?], therefore exactly the reverse 

 being the case. August 13 seems as conclusive a proof as one observer is 

 likely to obtain in a year's work." 



Of four observers on the same evening, two record No. 3, and the other 

 two appear not to have seen it. Taking them in chronological order, Neison, 

 9.5 to 9.15, records it as distinct ; Pratt, 10.30 to 12.30, did not observe 

 it; Ormesher, 11.0 to 11.30, does not show it in his drawing; Gledhill, 

 14'', records it as a bright disk : he also records 30. As these observations 

 are not contemporaneous, with the exception of Ormcsher's, having been 

 made while Pratt was observing, it appears, from its absence in both their 

 records, that from 10.30 to 12.30 it was really not visible ; and this tends to 

 support Mr. Pratt's idea that for the time it was hidden by something like 

 an obscuring medium. "What this could have been it is difficult to surmise. 

 The remark, however, of Neison that 30 Avas not to be seen between 9.5 

 and 9.15 is interesting in connexion with Gledhill recording both spots at a 

 later epoch, 14'', and also detecting five not seen by Pratt, viz. 3, 30, 9, 11, 

 18. Neison suspected he saw 14, not recorded by Gledhill nor Pratt, but 

 seen by Ormesher. Pratt saw 22, not seen by either of the others. The 

 case of 14 is a little perplexing ; it might, however, have been missed by 

 Pratt on account of the bad definition. "With regard to the greater number 

 of spots seen by GledhiU, two circumstances may have contributed to this 

 result, the larger aperture of Mr. Crossley's instrument and the epoch at 

 which Mr. Gledhill observed. It may possibly be found that the greater 

 number of spots recorded after the sun's meridian passage at Plato depend 

 upon the. steadiness and purity of the air mostly experienced after midnight. 



Suiisei and Sunrise on Plato, 

 Extracts from Mr. Pratt's notebook, 1870, Oct. 17, 11'' to \2\ Definl- 



