SCIENCE-GOSSIP. 



CHAPTERS FOR YOUNG ASTRONOMERS. 



By Frank 0. Bennett. 



(Continutd from p. 261.) 



JUPITER. 



During 1900 Mr. Stanley Williams thought the 

 spot was plainer, and that the reddish colour was 

 again appearing in its following or eastern half. 

 Immediately north of this spot there is a sort of 



The Planet Jupiter, Oct. 17th, 1880, 12 p.m., G.M.T. 



" bay," in the south tropical belt, which broadens 

 eastwards, forming a sort of dark elbow, which is 

 well shown in Rev. T. E. R. Phillips's drawing, fig. 4. 

 This is readily shown with a telescope of no more 

 than 2 inches aperture, and is traceable in many 

 drawings so far back even as September 1831, 

 when it was delineated by Schwabe. 



Bright spots have been seen on the planet, espe- 

 cially in the equatorial zone, from very early times. 



firmed when observers were attracted to tin- 

 planet by the advent of the great red spot. The 

 bright spots were found to overtake the red spot 

 and bo pass. Several such spots are beautifully 

 shown in fig. 3, bedding into the south tropical 

 belt. 



On October 17th. 1880, at midnight, the writei 

 found two small dark spots on the northern north- 

 temperate band, shown on fig. ."J, which is from a 

 drawing made at the time, by the aid of a 9J-inch 

 Calver reflector. These objects proved of greal 

 interest. Their colour was a deep Prussian blue; 

 they increased in number quickly, and were found 

 to gain even upon the white spots, so that there 

 were at. the sametimeon the planet three classes of 

 maculation, each yielding a different answer to the 

 question, "What is the period of Jupiter's rota- 

 tion '!" Mr. F. W. Denning determined the three 

 periods to be from 



Red spot 9 h. 55 m. 34 s. 



Bright spots . . . .9 h. 50 m. 5 s. 

 Dark spots, slightly exceeding . ( .i h. 48 m. s. 



This is not all ; these rates, as pointed out by 

 Denning, are not constant. For instance, in 1878 

 the red spot yielded a rotation period of 9 h. 55 m. 

 33:5 s., but in 1898 it had increased to 9 h. 55 m. 

 41'5 s., and this increase was not regular. A 

 variation is similarly noticeable in the case of the 

 bright spots. Thus it becomes evident that the 

 surface of the planet seen is by no means solid, 

 otherwise the motions would be regular. To 

 simplify the recording of observations, a zero 

 meridian was chosen, that passing the centre of 

 the disc at midnight on December 31st. 1871. Two 

 rotation periods were reckoned. System I.. 9 h. 

 50 m. 30 s. (877 o- 90 of Jovian longitude passing 

 the centre in 24 h.), and System II., 9 h. 55 m. 

 40-63 s. (S70°-27 passing in 24 h.) : System I. very 

 nearly accords with the period of the bright spots, 

 whilst System II. almost agrees with that of the 

 red spot. In dating drawings it is common to note 

 the longitude of the central meridian according to 

 both systems, as it simplifies the study of The 

 movements on the planets. Even a telescope of 



April 15th, 12 h. 10 m., G.M.T. May 6th, 10 h. 20 m., G.M.T. 



The Planet JuriTER in 1899. Drairn by Rev. Theodon E. R. Phillips 



Schmidt long since had pointed out that the 

 rotation of the planet was apparently found to 

 be shorter or longer when bright spots .or dark 

 ones were observed. This was abundantly con- 



3 inches aperture will show much of the beauty of 

 the belts if the air is good ami a power of from 

 130 to L80 employed. 



(7b be continued.) 



