522 BIBLIOGKAPHY OF HERSCHEl'S WRITINGS. 



Herschel, "W.: Synopsis or the Wiutixgs of — Contiuucd. 



A. D. Vol. p. 



1781 71 1*21 Two very good clocks were used; one having a deal pendulum rod 



and one a compounded one of brass and iron, both having a proper 



contrivance not to stoj) when winding up. The rate of going of my 



clocks I determined by the transit of stars. 

 121 Observations on Jupiter in the year 1778. February 24 — April 12. 



(See Plate V, Figs. 1 to 12, drawings oi Jupiter.) 



123 Observations on Jupiter in 1779. April 14 — April 23. See Plate V, 



Fig. 13 [misprinted 18]. 



124 Comparing the observations two and two the following times of one 



synodical revolution : 



gh 54m 56s 4 from an interval of 17 revolutions ; 



9*^ 55™ 20^ from an interval of 12 revolutions ; 



9^^ 55™ 24= from an interval of 15 revolutions ; 



gh 55m 4s g from an interval of 41 revolutions; 



gh 55m 403 from an interval of 1 revolution ; 



gu 54m 589_2 from an interval of 29 revolutions ; 



gh 54m 533,4 from an interval of 26 revolutions ; 



gh 51m 338 from an interval of 12 revolutions ; 



gh 51m 45s (5 from an interval of 12 revolutions; 



gh 50m 433 from an interval of 10 revolulions ; 



gh 51m igs.4 from an interval ot 22 revolutions; combining the 

 two preceding. 

 126 These several results are so various that it is evident that Jupiter is 

 not a proper planet for this critical purpose. This great variety 

 cannot proceed from inaccuracy in the observations; for, in my 

 opinion, it is not possible to make a mistake in the position of a spot 

 which shall amount to 5 minutes of time, as was proved by the ob- 

 servation of April 23, 1779. 

 126 The synodical revolutions have not been reduced to sidereal ones. 

 126 By a comparison of the difl'ereut periods it appears that a spot grad- 

 ually performs its revolutions in less time than it did at first. Ex- 

 amples of this are given. 



126 This is consonant with the theory of equatorial winds. 



127 Observations on Ifars in tho year 1777. (April 8 — April 27.) See Plate 



VI, Figs. 14 — 19, drawings of Mars. 



128 Observations on Mars in the year 1779. (May 9 — June 17.) Figs. 



20 — 23, drawings of Mars. 



130 Comparing the observations of 1779 two and two the i^eriods are : 



24h 38m is_5 from an interval of 2 revolutions; 

 24h 34m is_5 from an interval of 2 revolutions ; 

 24"^ 38™ 5''.9 from an interval of 36 revolutions ; 

 241^ 38™ 5^4 from an interval of 38 revolutions ; 

 24"^ 38™ 20^3 from an interval of 34 revolutions. 



131 Method of reducing synodic revolutions to sidereal (see Fig. 24, dia^ 



gram). 

 133 The sidereal iieriods from observations of 1777 and 1779 are : 

 2i^ 39™ 23^03 from an interval of 768 revolutions ; 

 24'' 39™ 18^94 from an interval of 768 revolutions; 

 24.^ 39™ 23^04 from an interval of 763 revolutions. 



134 24 '^ 39™ 21^.67 the adopted sidereal revolution of Mars on his axis. 



[Proctor's value, 24'' 37™ 22^715.] 



