The Lunar Eclipse of September 13. 225 



apparently in direct contrast with tliat to which I have just 

 referred, is, that Mr. De la Rue finds that he cannot photograph 

 with facility within some distance from the edge] of the termi- 

 nator. Objects that present the same luminous appearance to 

 the eye as those in the middle of the illuminated portion of the 

 disk, are yet only impressed with a very feeble degree of 

 intensity upon the photographic plate. 



Can these facts be of any assistance in reasoning upon the 

 character of the surface of our satellite ? For my" own part I 

 do not think any person who has been in the habit of observing 

 the Moon with an instrument of large aperture will be able to 

 accept the glacial theory. 



When using a telescope of ten or twelve inches aperture, pro- 

 tecting the eye from the great glare by a single-reflecting prism 

 solar eye-piece, the Moon's surface is seen to be almost entirely 

 covered with markings of a considerable variety of tone and 

 colour, many of these frequently changing in a few days, both 

 in shape and hue. Even with an instrument of six inches 

 diameter, some of these changes are easily perceptible. 



During the late eclipse, I devoted especial attention to the 

 colour of the Moon. It is a generally received opinion, that 

 when the obscuration has proceeded to the extent of two -thirds 

 or more of the surface, the obscured portion of the Moon 

 appears of a strong coppery red, and that the edge of the 

 shadow on the surface appears of a very decided blue. 



In Mr. Norman Lockyer's translation of Arnedee Guillemin's 

 "The Heavens," and in Keith Johnston's "Atlas of Astro- 

 nomy," diagrams of lunar eclipses are painted in chromo- 

 lithography in the colours I have stated. My observations 

 were made with Mr. Barnes's 10,] -inch silvered- glass speculum, 

 furnished with a reflecting prism, and an achromatic eye-piece. 

 Daring the whole time of the eclipse, I could never detect any 

 trace of colour upon the Moon, except what I ordinarily see 

 there. Looking through a four-inch refractor, I also observed 

 the same freedom from colour just noted. 



The colour stated to be seen on the part of the Moon under 

 eclipse is usually ascribed to the refraction of some of the solar 

 light as it passes through our atmosphere. I venture to sug- 

 gest that, when the colour is visible, absorption plays an 

 equally important part in producing it. This absorption would 

 affect principally the blue rays of the spectrum, and it would 

 be very small whenever our atmosphere is free from mist. 

 Now, on the night of the loth, as I have before said, the air 

 was remarkably clear, and this may possibly enable us to 

 account for the Moon's singular freedom from the colours 

 which seem to have been observed upon it on previous 

 occasions. 



VOL. XII. — NO. III. Q 



