OBSERVATIONS OP LUNAR OBJECTS. 89 



interesting : — " Some spots having at different times been observed as cra- 

 terlets, their character as volcanic is settled in my own mind. Whether 

 all spots are analogous I should be glad to know ; but on the supposition of 

 such similarity existing, the suggestion naturally arises whether the light 

 streaks be not scoriae or lava, or a mixture of both, resulting from the action 

 of the craterlets with which they seem to be connected." 



A comparison of the curves for the 20 lunations, April 1869 to November 

 1870, is suggestive of the craterlets being a distinct class of objects. The 

 phenomena characterizing the cratelets, as indicated by the curves, differ 

 very materially from the phenomena manifested by the spots ; for example, 

 in the correspondence of the maxima at the time of the supposed outbreak 

 of Aug.-Sept. 1869, we have an increase of visibility in spots, the behaviour 

 of the craterlets being altogether different. Certain neighbouring spots, to 

 which allusion has been made, declined greatly in visibility, and were very 

 seldom seen during a period in which the craterlets were almost always 

 visible ; and in connexion with this it may be remembered that craterlets 

 are characterized by high degrees of visibility, while of many spots which 

 have large ranges the normal degrees of visibility are low. 



That a connexion exists between the streaks and spots is, as Mr. Pratt 

 remarks, "self-evident ;" and Mr. Elger has shown that most of the spots 

 occur on the streaks. Now as both spots and streaks vary in brilliancy and 

 visibility, may not the steaks consist, as Mr. Pratt suggests, of ejecta from 

 the volcanic orifices of the craterlets? The increased brightness of the 

 streaks in the neighbourhood of the border has been frequently noticed, as 

 well as the unevenness of the floor. It may be possible that newly ejected 

 matter (especially if it be of the character of "broken glass," suggested, I 

 believe, by Dr. Huggins as explanatory of the appearance of Linne) may 

 reflect light more strongly, and thus contribute to the brighter appearance 

 of the streaks about the time at which the craterlets manifest increased 

 activity, and this may become so great as even to conceal the craterlets 

 themselves. On the other hand, although we are perfectly ignorant of any 

 meteorological or chemical action occurring at the surface of the moon, it 

 may be permissible to suggest that, if such action be possible, the reflective 

 power of the ejecta may become impaired, and the streaks in consequence 

 rendered less bright. 



It is exceedingly difficult to conceive that volcanic action can be in existence 

 on the moon's surface without "vapour" of some kind escaping from the 

 orifices. If this be the case, condensation must follow, and the orifice may be 

 covered by the condensed vapour, the upper surface of which may strongly 

 reflect the light and produce the appearance of a spot when not in a state of 

 actual eruption ; and this spot may be seen on a surface covered with ejecta, 

 the reflective power of which has been impaired since it left the orifice. 



One of the brightest portions of the floor of Plato is the S.E., which is 

 characterized by the "sector" or "fan." On the 10th of January, 1870, 

 !l[r. Gledhill observed as many as nine crater-cones on the eastern part of 

 the floor, viz. Nos. 1, 9, 11, 17, 4, 3, 30, 7, and 32. It is easily con- 

 ceivable that ejecta from some of these may be the perennial source of the 

 reflective power of the " sector." 



" It is, as far as I can see," says Mr. Pratt, " not at all proven that it is 

 impossible that they, the spots, may not be small acting volcanos at this 

 present moment ; and you will please credit me with having noted that, on 

 the 13th of May, although the spots were very greatly in excess of their 

 usual brightness, the relative brilliancy of the light streaks was not nearly 



