66 



REPORT 1871. 



cliangc takes place is as yet undetermined ; but there can be no question 

 tliat it is of the same nature as that of the appearance of the spots on Plato 

 greatly intensified. 



The result of the discussion may be briefly stated as being very strongly 

 suggestive of the existence of present lunar activity, the exact nature of 

 which requires further aud more extensive observations to determine. In- 

 timately connected with the spot-changes are the variations of appearance 

 and intensity of reflective power of the streaks and markings on the floor of 

 Plato. In the obsei-vers' and other notes which form the Appendix to this 

 Report will be found allusions to the connexion between the spots and streaks ; 

 but it manifestly requires a similar discussion of the streaks and markings to 

 arrive at a definite conclusion on the subject. Most of the observers have 

 furnished observations of these interesting phenomena, so that a discussion 

 of them could at once be proceeded with if it should be the pleasure of the 

 Association to carry on the inquiry. The principal results of the discussion 

 of the spot-observations relative to visibility, irrespective of solar altitudes, 

 and treated in pairs of lunations from April 1869 to November 1870, based 

 on 1594 observations during 20 lunations, are contained in Lunar Map Cir- 

 cular VIII. ; and some further remarks occur in a paper on the subject, 

 published in the Philosophical Magazine, March 1871. This discussion, on 

 an entirely difl'erent principle to that employed in the preparation of the 

 present Report, and leading to a similar result, tends to confer on both a 

 character in which confidence may be placed, for either without the other is 

 incomplete ; together they point to present lunar action as the originating 

 agency producing the phenomena. 



Although measurements for position of such delicate objects as the spots 

 on Plato are difiicult to execute, Mr. Gledhill has succeeded in obtaining 

 three sets of micrometrical measures, on September 13 and December 9, 

 1870, and on May 1, 1871, a combination of which has enabled me to draw 

 the outline of the crater, and to insert from these measurements four streaks 

 and the sector as seen generally by Mr. Gledhill. The streaks are ^, e, a, 

 and /3. The streaks ^ and e are rather westward of their places as given on 



