September 1, 1900.] 



KNOWLEDGE 



201 



do upon a later and more complete iuvcstigatiou. There 

 are indications tliat the spot has now begun to show 

 an accelerat-ed rate, my i-ecent observations being as 

 follows : — 



Daw. Trausit. Loiii-itmle. Diite. Tniiisit. LoiiiMlu.lc. 



1S>» u M. o liXXI. 11. M. o 



AiiK- 50 ... 6 33 ... 57.0 Jan. 8 ... 20 22 ... 56.4 



Sept. 6 ... 7 21 ... 56,4 Feb. 6 ... 19 26 ... 37.9 



,, 14 ... 5 59 ... 34.7 „ 20 ... 20 59 ... 37.5 



„ 16 ... 5 41 ... 56.5 ., 21 ... 16 53 ... 59.0 



Dec. 13 ...18 51 ... 38.2 Mar. 15 ... 15 5 ... 58.7 



„ 50 ... 17 54 ... 55.7 „ 17 ... 16 42i ... 59.5 



From thirty-five transits obtained in 1899, and from 

 others secured in 1S98, I found that the longitude of 

 the spot was increasing at the rate of O^.T per mouth 

 and that if this had been continued the marking wouKl 

 now be in 41°. 5, whereas its position is about 40°, so 

 that its rotation period this year has vei-y slightly 

 exceeded the rate (9h. 55m. 40.63s.) adopted for system 

 II. of Mr. Crommelius Ephcmerides, published in 

 Monthly Nutices. The spot now follows the zero meridian 

 about 66 minutes. Its eastern (following) end is 

 darkest, and easily seen, but the entire elli])tical outline 

 of the object can only be traced on a really first cla.'^s 

 night. 



There are a large number of equatorial spots visible 

 in the form of irregulai' white and dark patches which 

 are constantly undergoing changes. In the various 

 years when I have watched such of these markings as 

 border the south side of the Equator, their rotation 

 periods have been as under : — 



h. m. s. b. m. s. 



1880 9 50 5.8 1886 9 50 22.8 



1S81 9 50 8.8 1895 9 50 34.5 



1882 9 50 11.4 1898 9 50 23.6 



1886 9 50 14.3 1899 9 50 24.6 



The present period of these objects does not differ 

 materially from the rate exhibited in the two preceding 

 years. I believe that many of these objects have 

 existed for a very lengthy intei-val. They are probably 

 the same objects as were seen so prominently in 1879, 

 1880, and following years. Or we may go back further 

 still to the similar appearances figured by Gledhill and 

 others in 1869 and 1870, and even to the equatorial 

 spots delineated by Dawes, Huggins, Lassell, and others, 

 in 1858 and 1859. But there is a difficulty in identify- 

 ing the objects, as they are very numerous, and a break 

 of a few months has necessarily to occur in the obsei-- 

 vations every year, Jupiter being invisible near to the 

 sun. At the present time, though the mean rate of the 

 equatorial current is about 9h. 50m. 25s., the individual 

 spots differ in their rates from about 9h. 50m. 15s. to 

 9h. 50m. 3os. 



In the south temperate zone (in which the red spot 

 lies) the spots rotate at a regular rate of 9h. 55m. 19s. 

 I have noticed no change whatever in their motion 

 during the last twenty years, and, consulting old records, 

 I find that tliey have preserved the same period for a 

 great length of time. This is very curious, in view of 

 the singular variations of rate apparent in other 

 latitudes, and I believe these south temperate markings, 

 like many other features of Jupiter, are of considerable 

 duration. They suffer variations due to the atmospheric 

 vicissitudes under which they exist, but, though tem- 

 porarily obliterated, reappear in the same positions. 

 There are quite a large number of light and dark spots 

 in about S. latitude 28° or 30°, which have, I believe, 

 been visible during the last twenty years. They move 

 more rapidly than the red spot, and pass that object 

 just on his southern borders. Their conjunctions with 



the red spot aro exceedingly inti'icsi mi; iilu-iiiiiiirua. 

 In about 1880, when the rotation period of the latter 

 was 9h. 55m. 35s., the conjunctions occurred at interval s 

 of about 920 days, but in about 1898 the period was 

 reduced to 650 days. The interval separating the con- 

 junctions has, however, varied each year in consequence 

 of the marked change of velocity in the rate of the red 

 spot. I have traced back the conjunctions of two south 

 temperate dark .spots (nearly all observed) with the 

 red spot approximate! V as follows: — 



1. " H. 



1881, December. 1880, July. 



1884, April. 1882, December. 



1886. Muv. 1885, Feliniary. 



1888, Ajiril. 1886, November. 



1890, February. 1888, September. 



1891, December. 1890, August. 

 1893, September. 1892, June. 

 1895, July. 1894, AprilMay. 

 1897, April. 1896, February. 

 1899, .biiiuarv, 1897, November. 



»1900, October. 1899, Aut;ust. 



•1902, July. '1901, May. 



*1903, January. 

 * Ihese are the predict e<l dates of future conjunctions. 



Spot No. I. is at present in longitude 120°, wlulo 

 No. II. is in 203°. There are several other markings 

 of similar character; two of these were in conjunction 

 with the red spot at following times, viz.. No. III. 

 1892, October; 1894, August; 189G, May; 1898, 

 January; 1899, November; and No. IV., 1892, 

 March; 1894, January; 1895, November; 1897, 

 August; 1899, April. 



Further south of the south temperate spots tlu 

 current is more rapid, the rotation period being about 

 9h. 55m. 7s. 



In the north temperate region there is a remarkable 

 diversity in the proper motions of the objects. Here 

 we discover both the shortest and longest periods. 

 In north latitude, about 30°, the spots and condensa- 

 tions in the belts rotate in periods ranging from 

 9h. 55m. 50s. to 9h. 56m. Yet there is a narrow belt 

 in about latitude 25° N. which in 1880 rotated in 

 9h. 48m., and in less than 9h. 50m. in 1891. In this 

 belt there appear to be remarkable disturbances at 

 intervals of about ton years. There were outbreaks 

 from it in 1850, 1860, 1870, 1880, and 1890. Somy 

 details of these phenomena were described by the writer 

 in the Monfhhj Notice); for December, 1898. It is highly 

 probable that another eruption of spots will take place 

 from the same belt at the close of 1900, and be observed 

 when Jupiter becomes a morning star in February, 

 1901. Telescopic observers should therefore carefully 

 observe the planet at this time with a view to detect 

 the recurrence of the phenomenon. 



In the N. tropical zone of Jupiter, and bordering liio 

 N. edge of the northern equatorial belt, we find another 

 seat of very active and long continued energy. White 

 and dark spots are plentifully distributed along the 

 edge of the belt, and they do not partake in the rapid 

 velocity of the equatorial current, their period being 

 about 9h. 55m. 33s., though it varies to the extent of a 

 few seconds in different years. In 1899, the individual 

 markings differed in their periods to the extent of 18 

 seconds, and it was clearly manifested by all the ob.3Ci- 

 vations that one section of the belt, between longitude 

 140° and 260°, was moving much more rapidly than 

 the other part (.see Kev. T. E. R. Phillip's valuable 

 chart in Monthly Notices, Vol. LX., p. 214). 



The time seems come when all observations of Jupiter 

 made at each opposition of the planet should be com- 



