502 Changes in the Moan's Surface, [October, 



of white spot, 10 ; east edge of small crater distant from 

 east edge of white spot, 20. In Dr. Erck's (and Burton's) 

 drawing, the small crater is situated on the eastern part 

 of the white spot ; its position, measured on the same scale 

 as Dr. Huggins's drawing, is shown as follows : Length, 15; 

 small crater, 5, or one-third of the length of the white spot ; 

 west rim of small crater distant from west edge of white 

 spot, 8 ; east edge of small crater distant from east edge of 

 white spot, 2. Upon reducing the numbers for each drawing 

 to the same scale, we have, in 1S67, the eastern distance 

 double the western, and in 1873, the same distance is only 

 one-third that of the western. Equal weights being accorded 

 to the drawings (and we know that, in 1867, the then presi- 

 dent of the R.A.S., Professor Pritchard,* laid great stress 

 on the drawings of Dr. Huggins), it is clear that Linne has 

 undergone a change in the interval between 1866 and the 

 present time, and this circumstance of itself is enough to 

 induce renewed energy in as earnest an attack upon Linne 

 as took place in 1866 and 1867, especially as there is 

 now great probability of settling the disputed question of 

 change." 



It needs, however, only a comparison between the three 

 drawings taken by Mr. Browning on September 8, 1869, to 

 see that within the space of three hours Linne changed 

 from the aspect presented to Mr. Burton in 1873 to an 

 aspect more nearly resembling that presented to Dr. Huggins 

 in 1867. 



I pass now to the Floor of Plato. 



It was in November, 1861, that Mr. Birt communicated 

 his first series of observations of Plato to the Royal Astro- 

 nomical Society. On the same occasion he described an in- 

 strument for comparing colours, which he proposed to call 

 the homochromascope. In describing this instrument, he re- 

 marked that he had " found it necessary to devise some 

 means for comparing with various standards of colour 

 the tints of various portions, especially the dark-floored 

 craters, the extensive grey plains, and the more luminous 

 districts in immediate proximity with the raised craters." 

 I do not quote the description of the instrument, because I 

 am only concerned with its purpose ; and, in point of facl, 

 the instrument has not been completed, nor any substitute 



* We have evidence here of the mischievous results which must follow 

 from the election to high office in a learned society of a fellow thereof who, 

 whatever his qualifications may possibly be in other departments of knowledge, 

 has no special knowledge of the subject to which such society is devoted. 

 The supposition that any astronomical work by Dr. Huggins could gain 

 weight from comments by Professor Pritchard is amazingly absurd. 



