A. MATHEMATICS AND ASTRONOMY. 27 



zone b seems always to have had a color, which has been de- 

 scribed as being somewhat green and somewhat bhie. A 

 very similar color may be remarked in a thick block of ice. 

 The mean breadth of the equatorial band, c, was 9.7", vary- 

 ing, however, from 7.7" up to 13". Luminous spots were fre- 

 quently distinguished by him here and there, surpassing in 

 brilliancy all other portions of the planetary disk. The 

 variations of the bands b and c are especially noted by him. 

 Bullet. Soc. Imp. Naturalistes Moscoio, 1874, 185. 



THE ATMOSPHERE OF VENUS. 



Prof. Watson, of Ann Arbor, in an address to the French 

 Academy of Sciences, giving an account of his observations 

 of the transit of Venus at Pekin, stated that at the height of 

 about fifty-five miles, or one seventieth of the diameter of 

 Venus, the atmosphere of that planet was liable to cause 

 optical disturbance, such as would prevent the determina- 

 tion of the exact time of the real contact of its limbs with 

 the sun's limbs, and therefore interfere with the determina- 

 tion of the solar parallax. 12 A, XIL, 446. 



ON THE BRIGHTNESS OF THE SATELLITES OF JUPITER. 



Flammarion has made a series of observations of the bright- 

 ness of the satellites of Jupiter in 1874 and 1875, in which he 

 had in view the especial determination of the relative bright- 

 ness of each of these, and the determination of their own re- 

 ilecting powers, as well as the decision whether their bright- 

 ness is variable, and in what proportions. 



Amono; his observations he cites some showino^ that there 

 is an atmosphere about each satellite, and, again, that the in- 

 trinsic reflecting powers of these four moons is not the same, 

 but varies for each. Thus the fourth satellite is often dull 

 and hazy, and although larger than the first and second, it is 

 generally not so bright. Its surface is also not so white as 

 that of the other satellites. We may then conclude with 

 certainty that its substance, or at least its exterior surface, 

 has less reflective power than that of the other satellites. 

 Its brightness, moreover, varies considerably, and with no 

 definite periodicity, and without any relation to the position 

 of the satellite in its orbit: it is therefore not to any perma- 

 nent spots on its surface that it owes its changes, but rather 



