'THE PLANETS, ARE THEY INHABITED 1 



practised observers, with good telescopes. With, these, how- 

 ever, what appears near the poles, in instruments of inferior 

 power, as a dim shading of a yellowish-gray hue, is resolved into 

 a system of fine parallel streaks in close juxtaposition, which 

 becoming closer in approaching the pole, finally coalesce. 



In general, all the streaks become less and less distinct 

 towards either the eastern or western limb, disappearing alto- 

 gether at the limb itself. 



Although these streaks have infinitely greater permanency 

 than the arrangements of the clouds of our atmosphere, and are 

 even more permanent than is necessary for the exact deter- 

 mination of the planet's rotation, they are nevertheless entirely 

 destitute of that permanence which would characterise Zeno- 

 graphic features, such as are observed, for example, on Mars. 

 The streaks, on the contrary, are subject to slow but evident 

 variations, so that after the lapse of some months the appearance 

 of the disc is totally changed. 



12. These general observations on the appearance of Jupiter's 

 disc will be rendered more clearly intelligible by reference to the 

 telescopic drawings of the planet given in fig. 1 to 6. In fig. 1 is 

 given a telescopic view of the disc by Sir John Herschel, as it 

 appeared in the 20-fret reflector at Slough on the 23rd September, 

 1832. The other views were made by M.Madler from observations 

 taken in 1835 and 1836, at the dates indicated on the plate. 



The two black spots represented in figs. 2, 3, and 4, were those 

 by which the time of rotation was determined. They were first 

 observed by Madler, on the 3rd November, 1834. The effect of 

 the rotation on these spots was so apparent that their change of 

 position with relation to the centre of the disc, in the short 

 interval of five minutes, was quite perceivable. A third spot, 

 much more faint than these, was visible at the same time, the 

 distances separating the spots being about 24 of the planet's 

 surface. It was estimated that the diameter of each of the two 

 spots represented in the diagrams was 3,680 miles, and the 

 distance between them was sometimes observed to increase at 

 the rate of half a degree, or 330 miles, in a month. The areas 

 of these spots must therefore have been nearly equal to a fourth 

 part of the entire surface of the earth. The two spots continued 

 to be distinctly visible from the 3rd of November, 1834, when 

 they were first observed, until the 18th of April, 1835 ; but 

 during this interval the streak on which they were placed had 

 entirely disappeared. It became gradually fainter in January 

 (see fig. 4), and entirely vanished in February : the spots, how- 

 ever^ retaining all their distinctness. The planet, after April, 

 passing towards conjunction, was lost in the light of the sun j 

 40 



