Warren De La Rue to Faraday   22 December 1853

[De La Rue’s Letterhead] | 7 St Mary’s Road, Canonbury | December 22nd 1853

Dear Mr Faraday

Permit me to say that I am much flattered that so much of your attention has been bestowed on my drawing of Saturn¹ as to have called forth the conjectures respecting the relative positions of that planet’s rings which you are so good as to communicate to me.

The engraving represents the shadow of the planet on the rings correctly for a given epoch, but in other respects except for the position of the two satellites, it must be regarded as a summary of many observations:- for the moments of fine or even fair definition, on the most favorable night, are of too short duration to admit of a complete drawing being made, and I found it generally better to confine my attention to the recording of some one phenomenon only.

The inference I drew from the configuration of the shadow of the planet on the rings, coincides with your own, namely, that the middle ring is in a plane less elevated than the outer ring:- the outline, moreover, of the nebulous ring shows that it is more elevated than the two others, and on several occasions of fine definition I have had a distinct impression of its overlaying the middle ring as I have depicted.

I have repeatedly remarked that the outer and middle rings and the division between them were of different breadths at opposite ends of the same diameter, showing that their centres of gravity as well as their centres of rotation must be eccentric. This joined to their planes not being coincident must produce a complexity in their mutual perturbations and their action on the planet very interesting to the Saturnian mathematicians.

With respect to the probable section of the rings I would remark that on Oct. 16th of this year I observed this appearance

the shadow on the ring B being convex toward the planet - indicating its section to be thus

there was a faint penumbra visible beyond the dark shadow which was not itself so dark as the division between A & B. The night was as fine as any I have observed on. The shadow on the ring B was just visible on the Eastern side of the ball - but not on the ring A on that side.

One subject of interest with respect to Saturn is that the distance of the inner edge of the ring B from the planet’s centre is less than the drawings of the older observers would appear to indicate was the case in their day, and hence M. Otto Struve² who has studied the subject³ suggests that the ring may be gradually (or rather I should say rapidly) collapsing. He consequently felt desirous to have Huyghens⁴ object glass mounted in order to ascertain if the appearance was due to the telescope and in accordance with his request the Royal Society have as you know determined on so doing⁵. My own belief is that the older astronomers did not clearly observe the darker portions of the ring B and hence that its edge appeared to them more distant from the planet than it really was.

I enclose a few diagrams which I employed myself and furnished to other observers, and which, from being drawn out in accordance with the data given in the Nautical Almanac, so far as it goes, will show by comparison with my drawing how much I have had to change the relative diameters of the rings to agree with my impressions, which I would remark are confirmed in the main by M. Otto Struve’s micrometric measurements.

I must apologize for the length of this note which I fear will have tired your patience.

Very truly Yours | Warren De la Rue

Michael Faraday Esq | &c &c &c