i'i(^ 



Proceedings of Learjied Societies. 



[Jan. 1, 



equator, on the contrary, the curvature 

 is rather Ms than it is on Jupiter." 

 Upon the vvliole, therefore, tlie ihape of 

 the f;lobe of Saturn is not fuch as a ro- 

 tatory motion alone could have ^iven it. 

 " I fee," fays Dr. Hcrfchcl, " the quui- 

 tuple belt, the ciiviuon of the ring, a 

 Tcry narrow (hadow of the rin^ acrofs 

 the body, and another broader lliadow 

 of tlie body upon tlie followiiisr part of 

 the rins: : and unlcfs all thefe pui-ticulais 

 are very diftinttly vifiblc, wc cannot ex- 

 petl that our inflrument fliould lliow tlie 

 outlines of the phmet futficiently well to 

 preferve its peculiar formation.'' 



From the latcft obfervations it is in- 

 ferred : 1, that the breadth of the ring 

 Is to the fpace between the ring and the 

 planet, as about 5 to 4. 2, Tije ring 

 appears to be Hoping towards the body 

 of tlie planet, and the infide edge of it 

 is probably of a fphcrical, or perhaps 

 liypcrbolical, form 3. The Hiadow of 

 the ring on the planet is broader on both 

 fides than in the middle : this partly is u 

 confequence of the curvature of the 

 ring, wliich in the middle of its paflitge 

 acrofs the body hides more of the Iha- 

 dow in that place than at the fides. 4. 

 The fliadow of the body upon the ring 

 is a little broader at the north than the 

 fouth, fo as not to be parallel with the 

 outline of the body ; nor is it fo broad 

 at the north as to become fquare with 

 the dircftion of the ring. 5. The mod 

 northern dulky belt comes northwards 

 on both fides as far as the middle of the 

 breadth of the ring where it palTes be- 

 hind the body. It is curved towards the 

 fouth in the middle. 



" I viewed Jupiter," fays the Doctor, 

 " and compared its figure with that of 

 Saturn. An evident dilVerence in the 

 formation of the two planets is vifible. 

 To dillinguilh the figure of Jupiter pro- 

 perly, it may be called an ellipfoid, and 

 that of Saturn a fpheroid." 



With regard to tlie periodical changes 

 of the colonr of the polar regions of 

 Saturn, Dr. Herfcliel has ftn-merly ihewn 

 that an alternate periodical cliange takes 

 place in the extent and brightnefs of 

 the north and louth polar fpots on the 

 planet Mars ; on which he fuggclted an 

 idea that the caufe of the brightnefs 

 might be a vivid reflection of light from 

 frozen regions, and that the reduction of 

 the fpots might be afcribed to their be- 

 ing expofed to the fun; and he conceives 

 that, from the various obfervations that 

 he has made from time to time with 

 high magnifying powers, during a fpace 



beginning from June 2.'>, 1781, to June 

 3, 1806, fimilar concluiions may be 

 drawn with refpect to the appearance 

 of the polar regions of Saturn. In com- 

 jDaring his notes taken in 1781 witli ob- 

 fervations made in the fpring of the 

 prefent year, he lays, thefe contrafted 

 whh thofe wiiich were made when the 

 fouth-pole was in view, complete nearly 

 half a Satuniian year, and the gradual 

 cliangc of the coioui- of the polar re- 

 gions feems to be in a great meafarc af- 

 tertained. Should this be llill more 

 conlirmcd, there will then be fome foun- 

 dation for admitting thefe changes to be 

 the confequence of an alteration of the 

 temperature in the Saturnian, clinuites. 

 And if we do not afciibe the whiteiiefs 

 of the poles, in their winter feafons, im- 

 mediately to froll or fnow, we may at 

 leail attribute the ditferent appearance 

 to the greater liifpcnfion of vapour in 

 clouds, which, it is well known, reflect 

 more light than a clear atmofphcre 

 through which the opaque body of the 

 planet is moire vililile. The regularity 

 of the alternate changes at the poles 

 ought, however, to be obferved for at leall 

 two or three Saturnian years ; and this, 

 on account of their extraordinary length, 

 can only lie expetted from the fuccelhve 

 attention of allronomers. 



From obfervations on the change of 

 tlie colour at the polar regions of .Saturn, 

 arihng probably from a periodical alte- 

 ration of temperature, it is inferred that 

 Saturn docs polVefs an atinofphere, as 

 the frequent changes noticed can fcarcely 

 be afcribed to alterations of the furface 

 of the planet itfelf : " and if we add," 

 fays this learned aftronomer, " to this 

 confidcration, the changes I iiave ob- 

 ferved in the appearance of the belts, 

 or even the belts themfelves, we can 

 hardly require a greater confirmation 

 of the exiftence of fuch an atmofphere," 

 l'rget,ublc C/iemijiri/. 



Mr. Knight, who, according to Pro- 

 felTor Davy, has, in his papers laid be- 

 fore the lloyal Society, exhibited fome 

 of the fincli: fpecimens of pure analogies 

 everoft'ered to the public, appears again 

 as a contributor to this learned body. 

 The fubjett now is, the inrerted iiftion 

 of' the aUnirnous vfffeh of trees. He iias 

 already proved that the fluid by wliich 

 the various parts (that are annually add- 

 ed to trees, and herbaceous plants, whofe 

 organization is fimihir to that of trees,) 

 are generated, has previoully circulated • 

 through their leaves, either in the fame 

 or preceding fcufon, and fubfequently 

 defcended 



