The Moon. 57 



and very pale; in 1855, pale reddish-white and lilac; Dem- 

 bowski, in 1856, white and pale olive-blue. I found them, about 

 18505, with a 3 T 7 ^inch object-glass, white or a little yellowish 

 and tawny or lilac ; 1862*2, with 5f inches, the same colours, 

 but with very little contrast ; 6h seemed rather orange-tawny, 

 but became bluish when its light was materially reduced by 

 the passage of a thin cloud illuminated by the Moon. These 

 variations are probably due to instrumental and personal dif- 

 ferences ; but as this may not be the case in some other pairs, 

 an instance like the present deserves to be studied, with a 

 view of deciding between real and apparent changes of colour. 



This fine pair has been relatively fixed for 57 years, but has 

 a common proper motion. It is easily pointed out, in the 

 middle of a vacant space below the Great Bear's tail, by a long 

 line from Polaris through Alioth, or s Ursae Majoris, the 5th 

 star of that constellation, counting from right to left. 



For a reason the reverse of the last, we will take a fine 

 object in Cassiopea before it attains an inconvenient altitude. 

 This constellation, "the Lady in her Chan/'' is generally known 

 from its resemblance to the letter W, the top being towards 

 the Pole ; the student will find it about the beginning of August 

 in the evening, bearing N.E., at some distsnce to the right of 

 the Pole Star, but at a somewhat lower elevation. 



30. 7) Cassiopece. 9"'8. 87°-8 (1830-91). 7"-7. 108"3 

 (1854-17). 4 and 7*. Dull white and lilac. Herschel II. 

 and South gave red and green. Sestini, yellow and orange ; 

 Struve, flava and purpurea : sp Fletcher. Smyth calls this a 

 ". superb physical object/' with a period of about 700 years, 

 and a considerable proper motion of nearly 2" in R.A., and 

 Y in Declination annually. Eyre Powell reduces the period to 

 181 years. We have here a striking instance of the fact re- 

 ferred to under No. 25, the equal distance from our eye of stars 

 of very different magnitude. It is readily found by learning 

 the letters of the five conspicuous stars, which, beginning at 

 the right-hand end of the W, and reckoning backwards, are /?, 

 a, 7, 8, e. Our object is nearly in a line between a and 7, nearer 

 to a. Smyth could see it with two inches of aperture. 



THE MOON. 



The surface of our satellite is at once a very easy and a 

 very interesting object of telescopic research. As not merely 

 the general arrangements of its lighter and darker portions, 

 but even the greater irregularities of its " terminator/' or 

 boundary of light and darkness, are visible to the naked eye, 

 it is evident that the smallest telescope will suffice to give us 

 some curious information ; while instruments of moderate size, 



