552 BIBLIOGRAPHY OF HERSCHEl's WRITINGS. 



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



A. D. Vol. p. 



17i)4 84 48 On the rotation of the planet Saturn vpon its axis. By William Her- 

 schel, LL. D., F. R. S. Read January 23, 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 present 

 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 cliange for the last two months. 



48 I give the observations upon 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 reflector, having 

 found that a 7-foot reflector was adequate to my purpose. 



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



were used with an eye-glass of -fV 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 [formerly]. 



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 diflereuce really exists. 



53 Observation njyon the double ring of Saturn. 



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

 very bright close to the dividing 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 BemarJc on the shadow 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 broader there than in the middle, 

 the ends turning toward the south. 



56 The five old satellites are all seen with a i^ower of 60 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 little brighter than they used 

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

 ring upon Saturn is perfectly black, like the shadow of Saturn upon 

 the ring. The shadow of the ring ux^on Saturn on each side is bent 

 a little southward. 



58 Trial of concave eye-glasses. 



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

 vex glasses. 



59 Determination of the period of the rotation of Saturn. Explanation of 



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

 tions. 



60 The first trial gives 10'' I.'')'" 40' for the time of 1 revolution. 

 The second trial gives lO*" 10™ 51^ for the time of 1 revolution. 



61 The third trial gives LO'' 17'" 54^ for the time of 1 revolution. 

 The fourth trial gives 10'' 17'^' 6^ for the time of 1 revolution. 



