On the Satellites and Belts of Jupiter. IJ5 



to observe if there were any small stars in its vicinity; 

 knowing that there are many nebula; belonging to that part 

 of the galaxy, or milky way, which runs through the pre- 

 ceding constellation Sagittarius, and by the precession of 

 the equinox border upon the sign of V? ; but could not 

 discern any : for the two satellites I had observed were in 

 the places I saw them by my naked eye, as well as the two 

 other lesser ones ; that is to say, one of the outer ones was 

 on the eastern and the other three were on the western side 

 of their primary, thus : q „ c 



o 

 1 did not take particular notice of the belts at this time, 

 because I was too much interested with the novelty of the 

 satellites: but an idea has often occurred to me respecting the 

 rationale of their mutations (i. e. of the belts) which I think 

 may (at least analogically speaking) elucidate the phenomena 

 of their fluctuation. For instance : when the sun is about to 

 pass from either hemisphere into the other, the rarefaction 

 of vapours consequent upon his presence causes so great a 

 commotion in the atmosphere as to produce a continual 

 current of wind, and to carry the clouds in one direction 

 throughout most part of the torrid zone of our earth (called 

 a monsoon, or general trade wind, &c). Now, if we were 

 to be elevated to a great height above our atmosphere, it is 

 plain, I think, that this current must give the clouds a lineal 

 direction, by which they would assume the appearance of 

 one or more belts or girdles passing across the equatorial 

 parts of the earth, and which belts would change their form 

 and dimensions to an aerial observer in six months in a si- 

 milar manner to those of Jupiter in 5$- years (equal to half 

 a year in that planet) : I therefore think it but fair reason- 

 ing to suppose that Jovian trade winds, or something equi- 

 valent thereto, carrying his clouds in an equatorial direction, 

 produce these mutations on the face of that planet which we 

 call belts, and for which phaenomena I have never seen any- 

 colourable conjecture. If these ideas meet your approbation, 

 and you think them worthy of insertion, they are much at 

 your service — From yours respectfully, 



Southwark Philosophical Society, j OHN C NAUT 



215, Tooley-street. JOHN SNAHT. 



XXIX. Me- 



