Saturn’s Ears

Dear Benedetto,

You asked what became of the two companions I once drew beside Saturn, and whether I regret having published them. I have been through the old notebook again, the one from January of 1611, and I will tell you plainly what I found.

The hypothesis was this: that Saturn carried two small globes, fixed to it, touching it on either side. I drew them as ears. The instrument showed ears; the hypothesis accounted for the ears; for six years the account held. Then in 1612 the ears were gone. Not dimmer - gone. The globe of Saturn sat alone in the field, round and bare, and the hypothesis of the fixed companions could not survive it, because a body fixed to a body does not detach and vanish. I wrote at the time that I did not know what to say, and I meant it.

But here is the half-formed thought I want to hand you. The dead hypothesis did not leave nothing behind. It left a constraint. Whatever Saturn is, it must be capable of showing two lobes in 1611 and none in 1612, from the same instrument, at the same magnification, observed by the same eye. Any future account - and I suspect the true one will involve some figure that changes its aspect with our changing line of sight - must pass through that record. The ears were real appearances, whatever they were in substance. A discarded explanation is not a discarded observation. The one dies; the other stands in the log, dated, and every hypothesis to come must reckon with it.

I think we throw away too much when we throw away a refuted theory. The geocentrists built a machine of spheres so elaborate that it could not produce the full phase of Venus under any configuration whatever, and that failure was worth more to me than all its successes. The failure narrowed the world. So too the ears of Saturn: they narrow it still. Whatever the truth is, it is not two fixed globes, and it is not nothing.

The notebook entry for 26 July 1616 reads: Saturn has two handles attached on either side, faint.