April i6, 1896J 



NATURE 



559 



by two seconds. The mean result for the surface 



material of Jupiter between latitudes 40" to 85° north 

 gave gh. 55m. 38"9s. ± r2os., this being the length of a 

 sidereal rotation expressed in mean solar time. Observa- 

 tions of some dark, well-defined spots in 1891 gave as a 

 value for the period of rotation gh. 55m. 38'5s., while 

 Denning found (1894-5) the value gh. 55m. 390s., still 

 closer to that given above. 



It will be noticed that up to the present the observa- 

 tions of Stanley Williams do not corroborate a reduction 

 in the rate of rotation in higher latitudes, as would be 

 expected from Lohse's discussion. The observations of 

 the two may, however, be harmonised to some extent if, 

 as before, one supposes that they observed markings at 

 different levels in the atmosphere of the planet. If this 

 were so, then very probably Stanley Williams generally 

 watched those markings in the higher regions, while the 

 spots observed by Lohse were situated at a far deeper 

 level, and in which perhaps were strong currents. 



A spectroscopic investigation of great interest is that 

 due to Dr. Belopolsky, who undertook the determination 

 of the velocity of a point in the equatorial region of 

 Jupiter. The method of procedure was as follows. He 

 assumed that the equatorial region of this planet made 

 one rotation every gh. 50m. ; knowing the angular 

 diameter of the disc from measures made with the micro- 

 meter, he then calculated the velocity of a point on the 

 equator, the resulting velocities being 12 and 13 kilo- 

 metres per second, according to the special value of the 

 diameter used. The second part of the work consisted 

 in observing the east and west limbs of the planet spectro- 

 scopically, using the principle of Doppler to find out the 

 displacement of the lines due to the velocities in the line 

 of sight. The value he obtained was 11*4 kilometres per 

 second, a number smaller than that v/hich would appa- 

 rently be expected. The great difference between the 

 observed and computed velocity may be due to errors of 

 observation, but its magnitude calls for another explana- 

 tion. Belopolsky himself prefers to account for this 

 difference by regarding it as a result of refraction, an 

 assumption which is quite permissible, as Schmidt has 

 shown in his theory of the sun. 



Perhaps the best idea of the drift of the Jovian surface 

 can be gathered from a summary of the determinations 

 of the length of the period made from surface-markings 

 at different Jovian latitudes. This table we owe to Mr. 

 Stanley Williams, and it appeared in a previous number 

 of N.VTURE (vol. liii. p. 376). It will be noticed that the 

 nine zones represent practically nine distinct currents 

 in the planet's atmosphere, their boundaries being de- 

 scribed as sharply defined. These currents completely 

 encircle the planet, and have an east and west direction; 

 very little indications of motion towards the poles having 

 been noticed. 



Period 



Curiously enough, the zone numbered VII., which re- 

 presents the red-spot zone, has not an equivalent in the 

 northern hemisphere, that numbered III. having a much 

 quicker drift. 



Apropos of this red spot zone, we may mention that 

 Mr. Stanley Williams expresses the opinion that the 



NO. I 38 I, VOL. 53] 



mysterious red spot acts in the same way as, and has 

 some analogy to, an island in a river {KnowIedgCy April). 

 The spot lies between the south equatorial belt and the 

 south temperate belt, and as the white material between 

 these two belts drifts past the red spot with a velocity of 

 sixteen miles per hour, it is obliged to force a passage 

 round the spot. Most of this white material passes to 

 the north side of the spot, making a depression in the 

 south equatorial belt ; but some of it finds a way 

 through a very narrow channel on the south side. There 

 is less resistance to the passage of the material on the 

 north side of the spot, probably for the reason that the 

 surface is most plastic in the equatorial regions. As the 

 channels on the north and south sides of the red spot are 

 together narrower than the main channel, there is a 

 heaping up of white material on the following side of the 

 spot and in the channels, and this seems to possibly 

 explain the bright annulus which is frequently seen 

 encircling the red spot. The union of the two currents 

 produces a commotion on the preceding side of the spot, 

 giving rise to the hazy patch which is usually visible in 

 that position. As a working hypothesis, the idea seems 

 likely to be of use in suggesting observations, but it is 

 admittedly difficult to conceive how such an effective 

 obstacle as the red spot can drift about in the way it has 

 done. 



The latest observations regarding Jupiter's surface 

 thus show us that the whole disc of vapour that we see is 

 in a state of slow circulation in currents more or less 

 parallel to the equator. The rifts that appear to traverse 

 the disc in the north and south direction may be the 

 effects of a slow circulation in this direction. 



The east and west currents do not then necessarily 

 increase their rate of rotation the nearer the equator is 

 approached ; but there may be zones of quicker rotation, 

 followed by zones of slower rotation before the equator 

 be reached. It will thus be seen that a very accurate 

 value of the period of rotation of Jupiter is difficult to 

 determine, since the several drifts are in relative motion 

 one with another. W. J. S. L. 



THE LIFE OF JOSEPH IVOLF.^ 

 T T seems now to be rather in fashion to write lives of 

 -^ persons still in existence. In some cases, such as 

 the present, there is little to be said against this practice ; 

 in others, it may be open to very serious objections. But 

 when the biography of a living person is given to us by 

 an intimate personal acquaintance, we have, at any rate, 

 one advantage : it may be assumed that the narrative 

 has been more or less supervised by the person to whom 

 it relates, and that the facts and incidents stated are 

 generally correct. Such, we know, is not always the 

 case with biographies of departed heroes. 



Joseph Wolf, well known to all zoologists as the 

 " Prince of Animal Painters," and one whom savants 

 and artists alike agree to class as "absolutely unrivalled" 

 in his special department, was the son of a German 

 farmer, or what was formerly called in the south of 

 England a "yeoman," farming his own land at the little 

 village of Moerz, between Treves and Coblentz. Born in 

 1820, Wolf was sent to the village school at Metternich, 

 where his observant habits and " superior skill in draw- 

 ing maps " told favourably with the master. But to his 

 fellow-scholars a boy who "refrained from bird-nesting 

 on principle," and would fight any of them in defence of 

 a nest of young birds, was somewhat of a puzzle. Here, 

 however, Wolf had many opportunities, both during his 

 school-days and in the course of the initiation into farm- 

 life which followed, of studying nature. A fine wild 

 country was around him, where beasts and birds were 

 abundant, and he soon taught himself to observe them, 



1 "The Life of Joseph Wolf, .\nim.il Painter." By A. H. Palmer. 

 Illustrated. Pp. .wiii -J- 328. (London : I^ngman.s, 1895.) 



