232 Proceedings of Philosophical Societies, [Sept. 



known, employing the power 540 : Professor Struve describes 

 both the instrument and the manner of observation ; but it will 

 be simply necessary here to record the results for the planet's 

 mean distance, which are as below : viz. 



1. The external diameter of the external ring = 40'''*215 



, 2. internal ditto. 35 -395 



■''^.''' external internal ring 34*579 



4. ^ ■ internal ditto. 26 -748 



6. " equatorial diameter of Saturn 18 -045 



6. breadth of the external ring 2 -410 



7. ditto chasm between? 0*408 



the rings 3 



8. ditto internal ring 3 '915 

 y. Distance of the ring from Saturn 4 -352 



10. The equatorial radius of Saturn ......;•...,, 9 '022 



The mean value of the inclination of the ring to the ecliptic, is 

 28^ 5'*9, with a probable error not exceeding 6'*9. 



M. Struve has detected no trace of a division of the ring into 

 many parts ; but he observes that the outer ring is much less 

 brilliant than the inner. The five longest-known satellites are 

 readily distinguished, through Fraunhofer's telescope, even in 

 the illuminated field. The 4th appears like a small disc, diame- 

 ter O'^'TS. M. Struve saw the 6th several times ; but he has 

 never seen the 7th; of whose existence indeed Schroeter enter- 

 tains doubts. 



The same paper also details the results of micrometrical 

 measurements of Jupiter and its satellites, made with the same 

 instrujfnents, and with the same power 540, or from thence to 

 6OO! The mean results at the mean distance of the planet from 

 the earth, are, 



1. Jupiter's major axis 38'M42 



2. minor axis 35 -645 



3. compression -0728 or-pTTT 



4. Meandiam. "V's 1st Sat. .. 1*018 



5. 2d -914 



6. 3d 1 *492 



7. 4th 1 -277 



Schroeter and Harding have often imagined, that they have 

 detected a deviation of Jupiter from the elliptical form; and so 

 thought Struve at first ; but a closer examination enables him 

 to explain the illusion. On March 7th this year, he thought 

 the diameter which extended from 61°*4 lat. preceding S. to 

 61°*4 lat. following N. was obviously smaller than the ellipsis 

 would allow. But the micrometric measurement proved that 

 that was not the case. That evening the major axis, A, was 

 44''- 75; the minor axis, B, was 4r^-72 ; and the diameter in 

 question takeu with the ^ame micrometer was 42''* 34. Calling 



