388 Moon Colours. 



MOON COLOURS. 



The observations on the lunar crater Linne, have established 

 beyond a doubt, firstly, that changes, of an apparently volcanic 

 nature, still occur on the surface of our satellite, and secondly ) 

 that alterations take place at a rate sufficiently rapid to hold 

 out the hope that even a brief period of accurate study and 

 comparison may suffice to ascertain and demonstrate their 

 occurrence. It may be that the enormous craters which form 

 such conspicuous features in lunar scenery, belong to a past 

 epoch, when the crust of the moon was in a plastic state, and 

 fresh operations on so grand a scale may not be likely to occur. 

 There would, however, remain the probability of our witnessing 

 alterations which, if less gigantic, might be equally instructive, 

 and for their ascertainment two things are requisite, an exact 

 knowledge of forms and a similar knowledge of colours as they 

 exist at any given time, and as they are modified by local 

 action. The great map of Beer and Madler, the maps of 

 Lohrmann, etc., have done much for lunar forms, and the 

 British Association map, on which Mr. Birt is engaged, will be 

 of the highest value to future observers, although we must 

 observe that the Moon Committee cannot arrive at a satis- 

 factory result if they leave Mr. Birt to work with a telescope 

 ridiculously small, and which cannot possibly show one quarter, 

 perhaps not one-twentieth, of the minute objects he is expected 

 to lay down with mathematical accuracy. An instrument — say 

 a silvered glass reflector — of at least ten or twelve inches, must 

 be regarded as indispensable, and we hope we may soon hear 

 that he will be provided with a telescope equal to the majority 

 of those which are employed in public and private obser- 

 vatories. 



All astronomers perceive the importance of noticing and 

 recording changes of form, but changes in colour may prove 

 nearly as important, and no means of estimating them have yet 

 come into general use. Admiral Smyth's Sidereal Chro- 

 matics suggested at the time of its publication the propriety 

 of establishing similar standards for the moon, for it is clearly 

 not sufficient to study variations in luminosity without also 

 taking cognizance of modifications of tint or hue. 



Few observers can have watched the lunar seas and plains 

 for any length of time without finding evidence that colour 

 changes do occur. The green tint noticed on some spots 

 seems especially to vary, and is often invisible, while modi- 

 fications appear in the neutral tint blues or ochrey browns. 

 Although we see the moon as an opaque object, its tones of 

 colour are extremely difficult to imitate by opaque pigments. 



