126 Mr. hsrschel’s AJlrcnomical Obfervatwns 
Thefe feveral refults are fo exceedingly various, that it is evi- 
dent Jupiter is not a proper planet for the critical purpofe of a 
comparative view of the diurnal motions ; nor can this great 
variety proceed from any inaccuracy in the obfervations : for, 
in my opinion, it is not well poffible to make a miftake in the 
fituation of a fpot that lhall amount to fo much as five minutes 
of time* The obfervation of April 23, 1779, was made with 
a view to afcertain this point, when it was found that five mi- 
nutes of time made a fenfible difference in the fituation of a 
fpot when near the center. 
If we reduce the fynodical revolutions to fydereal ones, the 
refult will be fo little different from the above, that I have not 
thought it worth while to do it in this place* By a comparifoii 
of the different periods it appears, that a fpot which is carried 
about in the atmofphere of Jupiter generally fuffers an accelera- 
tion* or, which is the fame thing, performs its revolutions by 
degrees in lefs time than it did at firft ; for the fpot obferved in 
1778 moved at the following rates. From February 25. to 
March 2. in 9 h. 55' 20" ; to March 3. nearly the fame; to 
March 14. in 9 h. 55' 4" ; from March 2* to March 3. in 
9 h. 55' 40"; to March 14. in 9 h. ^' 58" ; from March 3. 
to March 14. in yh. 54' 53". In 1779 a fpot moved from 
April 14. to April 19. at the rate of 9 h. 5 1 7 45 '' ; to April 23* 
in 9 h. 51' 24"; and from April 19. to April 24. in 9 h. 50' 48" ; 
all which is agreeable enough to the theory of equatorial winds, 
fince it may probably take up fo me time before a fpot can acquire 
a fufficient velocity to go as faff as thofe winds may blow. And, 
by the by, if Jupiter’s fpots fhould be obferved in different 
parts of his year, and be found in fome to be accelerated, in 
others to be retarded, it would almoft amount to a demonftra* 
tion of his monfoons and their periodical changes; but if his 
7 axis 
