552 BIBLIOGRAPHY OF HERSCnEL'jS WRITINGS. 



Herschel, W.: Syxopsis of the WiaTtxGS of— Coutinued.. 



A. D. Vol. p. 



171)4 84 48 On the rotation of the planet Saturn upon its axis. By William Her- 

 schel, LL. D., F. R. S. Read January 2:3, 1794. 

 48 In a late paper I pointed out an analogy which might lead us to sur- 

 mise that Saturn had a quick rotation on its axis. I can at jiresent 

 announce the reality of that rotation by means of observations of 

 154 revolutions of the planet. 

 48 The belts of Saturn that I have been observing seem to have under- 

 gone no material change for the last two months. 

 48 I give the observaticms u^jou which my computations have been 



founded, entire. 

 49-59 Observations on the belts of Saturn. 



50 [Foot-note.] In the course of these observations I made 10 new ob- 



ject specula and 14 small plain ones for my 7-foot retlector, having 

 found that a 7-foot reflector was adequate to my puri)ose. 



51 [Foot-note.] These objectives were from 84 to 88 inches focus, and 



were used with an eye-glass of -^^ of an inch focus, the power thus 

 being from 280 to 293. 



52 I took care to bend my head so as to receive the picture of the belt 



in the same direction upon the retina as I did [foi'uierly]. 



52 [Foot-note.] This was a precaution that occurred to me, as there 



was a possibility that the vertical diameter of the retina might be 

 more or less sensible than the horizontal one; but I had no reason 

 afterward to suppose that any such ditference really exists. 



53 Observation upon the double ring of Saturn. 



The outer ring is less bright than the inner ring. The inner ring is 

 very bright close to thedividing space; andat about half its breadth 

 it begins to change color, gradually growing fainter. 



54 There is a dry wind and the telescope will not show objects as dis- 



tinct as when moisture is discharged from the air by the precipita- 

 tion of dew. 



55 liemark on the shadoiv of Saturn and its rings. 



On the ring is the shadow of the body. The shadow of the ring upon 

 the body of the planet close to the ring is not parallel to the ring 

 at the two extremes, but a little bi'oader there than in the middle, 

 the ends turning toward the south. 

 5G The five old satellites are all seen with a power of GO on a 10-foot re- 

 flector. 



57 Observations of the south pole of Saturn and the shadow of the ring. 



The south polar regions of Saturn are a 1 ittle brighter than they used 

 to be; they are almost as bright as that belt. The shadow of the 

 ringui>on Saturn is perfectly black, like the shadow of Sa/ urn upon 

 the ling. The shadow of the ring upon Saturifon each side is bent 

 a little southward. 



58 Trial of concave eye-glasses. 



With regard to the fleld of view, they are full as convenient as con- 

 vex glasses. 



59 Determination of the pcrh)d of the roiuiion of Saturn. Explanation of 



Plate IX and the method of obtaining the period from the observa- 

 tions. 

 GO The first trial gives 10'' 15™ 40^ for the time of 1 revolution. 



The second trial gives 10'' IG"' 5P ior the time of 1 revolution. 

 61 The third trial gives 10'' 17"' 54' lor the time of 1 revolution. 

 The fourth trial gives 10'' 17'" & for the time of 1 revolution. 



