ON THE PROMOTION OF SCIENCE. 



4J 



at present, and which is not much different from 

 iris appearance for several years past. These 

 appearances may be seen by a good achroma 

 tic telescope, magnifying from 80 to 150 times. 

 These views demonstrate, that changes of con 

 siderable magnitude are occasionally taking 

 place, either on the surface or in the atmosphere 

 of this planet, which it would be of some impor 

 tance to ascertain, in order to our acquiring a 

 more intimate knowledge of the physical consti 

 tution of this globe. Now, were a number of 

 observers, in different places, to mark these ap 

 pearances, and to delineate the aspect of this 

 planet during the space of two or three periodi 

 cal revolutions,* marking the periods of the dif- 

 feient changes, and noting at the same time the 

 positions of his satellites it might be ascer 

 tained, whether these changes are occasioned 

 by tides, which are differently affected accord 

 ing to the position of his moon?, or, by immense 

 strata of clouds, or other changes that take 

 place in his atmosphere, or by some great phy 

 sical revolutions which are occasionally agita 

 ting the surface of this planet. The observers 

 of such facts behoovod to be numerous, in order 



The annual or periodical revolution of Jupiter is 

 completed in about eleven years and ten months. 

 6 



that the deficiencies of one might be supplied by 

 another, and the general conclusions deduced 

 from a comparison of all the observations taken 

 together ; and it would be requisite, that the 

 places of observation be in different countries, 

 that the deficiency of observations in one place, 

 occasioned by a cloudy atmosphere, might be 

 compensated by those made in the serene sky 

 of another. Such a series of observations, al 

 though they should not lead to satisfactory con 

 clusions in relation to the particulars now stated, 

 could scarcely fail of throwing some additional 

 light on the nature and constitution of this 

 planet. 



With respect to the planet Venus, the author 

 some time ago ascertained from observation,! 

 that this planet may be distinctly seen in the 

 day-time, at the time of its superior conjunction 

 with the sun, when it presents to the earth a 

 full enlightened hemisphere ; provided its geo 

 centric latitude, or distance from the sun s 

 centre at the time be not less than 1 43 / . This 

 is the only position (except at the time of a 

 transit, which happens only once or twice in a 



+ See Nicholson s Phil. Journal, vol. xxxvi. for 

 Oct. 1813. Edin. Phil. Journal, No. v. for July 1820. 

 -Monthly Mag. Feb. 1814, and August 1820, p. 62. 

 Scots Magazine for 1814, p. 84, &c 



