252 



REPORT 1872. 



curious than I had seen it before, and totally different from my former 

 sketches." 



Fig. 5, August 17, 1869. — In this figure we see a very considerable exten- 

 sion of the dark portion of the floor, the spot No. 6 still marking the position 



Fig. 4. 



Fig. 5. 



Plato, 1860, August 16.— H. Pratt. 



Plato, 1869, August 17.— H. Pratt. 



of the western edge of the eastern leg of the W of the 16th. On the 17th we 

 find this leg had extended quite to the eastern border ; indeed the whole of 

 the northern boundary of the dark portion had become extended to the N., 

 N.W., and W. border ; at the same time the opening between the eastern 

 and middle legs unveiling the lighter floor (?) had become extended, so as to 

 include spots Nos. 3 and 19, and to exhibit (?) spot No. 13. If this were so, 

 it could only have been eff"ected by a separation of the darker substance, 

 whatever it was, which, spreading outwards towards the border of Plato, pro- 

 duced the difierent configuration observed on the 17th. This opening from 

 the S.W. part of the floor to the east border and sector was seen by Mr. 

 Gledhill on September 25, 1869 (see post, p. 295, and fig. 9, p. 263). 



In the southern part of the floor we have another opening, apparently in 

 the neighbourhood of spot No. 1, which joined the opening effected in the 

 northern part at its western end, the N.W. arm of trident e ; and, simultane- 

 ously with this opening, the dark substance near spot No. 3 overspread a 

 portion of the opening between the western and middle legs, by which the 

 stem and north-western arm of the trident was produced. 



That part of the darker portion just S.W. of spot No. 1 must have under- 

 gone the greatest change in its disposition, inasmuch as not only was an 

 opening made from No. 1 to beyond No. 14, but the substance itself must 

 have increased ; for there can be no doubt that the area covered by the darker 

 portion on the 17th exceeded that covered on the 16th. The effect of this 

 extension was the production of the S.E. and middle arms of the trident, or, 

 at least, the rendering of them apparent as compared with the 16th. 



Looking at the position of spot No. 1 in connexion with the three arms of 

 the trident, can it be possible that emanations from this crater tended to 

 preserve the radiating openings marked by the figure so well observed from 

 the 17th to the 28th inclusive? 



In reference to August 17, Mr. Pratt has the following remarks : — " This 

 [the floor] was very remarkable : resolved to give it especial attention, and, 

 after some application, succeeded in adding piece to piece till a sketch was 



