APPEARANCES OF THE CELESTIAL BODIES. 423 



quently, and perhaps generally, visible in the day ; and together with the 

 moon, must exhibit a very interesting object. The atmosphere of Venus is 

 supposed to be nearly like our own, or somewhat more rare. 



The inhabitants of the moon, if the moon is inhabited, must be capable 

 of living with very little air, and less water : there is reason to think their 

 atmosphere less than a mile high, and it is never clouded : so that the sun 

 must shine without intermission for a whole fortnight on the same spot, 

 without having his heat moderated by the interposition of air, or by the 

 evaporation of moisture. The want of water in the moon is not, as some 

 have supposed, the necessary consequence of the want of an atmosphere ; 

 but it is inferred partly from the total absence of clouds, and partly from the 

 irregular appearance of the margin of the moon, as seen in a solar eclipse : 

 no part of it being terminated by a line sufficiently regular to allow us to 

 suppose it the surface of a fluid. The earth must always appear to occupy 

 nearly the same part of the sky, or rather to describe a small oval orbit round 

 a particular point, exposing a surface 13 times as great as that of the moon 

 appears to us. This large surface, suspended, with phases continually 

 changing, like those of the moon, must afford, especially when viewed with 

 a telescope, an excellent timepiece ; the continents and seas coming gradu- 

 ally and regularly into view, and affording a variety equally pleasing and 

 useful. To us such a timepiece would be of inestimable value, as it would 

 afford us an easy method of discovering the longitude of a place, by com- 

 paring its motion with the solar time: but in the moon, the relative 

 position of the earth and sun, or of the earth and stars only, would be 

 sufficient for determining the situation of any place in sight of the earth ; 

 if, however, there are no seas and no navigation, astronomical observations 

 of this kind would be of very little utility. The assistance of the earth's 

 phases in the measurement of time might, however, still be very useful for 

 many purposes, to the inhabitants of the nearer half of the moon ; and 

 probably the remoter part is much deserted, for in their long night of half 

 a month, they must be extremely in want of the light reflected from the 

 earth, unless the inhabitants have the faculty of sleeping through the whole 

 of their dark fortnight. The surface of the moon appears to be very rocky 

 and barren, and liable to frequent disturbances from volcanos. These 

 have been supposed to project some of their contents within the reach of the 

 earth's attraction, which they might easily do, if they could throw them out 

 with a velocity of about eight thousand feet in a second, which is only four 

 times as great as that of a cannon ball : and these stones, falling through 

 the atmosphere, might very possibly generate so much heat, by compressing 

 the air, as to cause the appearance of fiery meteors, and to fall in a state of 

 ignition. The appearance of the moon, as viewed through a good telescope, 

 is extremely well imitated by Mr. Russel's lunar globe, which is also capa- 

 ble of exhibiting, with great accuracy, the changes produced by its libra- 

 tions. 



The climate of Mars is as much colder than ours, as that of Venus is 

 .warmer ; in other respects there is no very striking difference : the incli- 

 nation of his axis to his ecliptic being nearly the same as that of the earth's 

 axis, the changes of seasons must be nearly like our own. Dr. Herschel 



