Crown Glass Disc, March Fourteenth

Filed under: Apprenticeship, Instruments, Refraction - subheading, The Correction of First Impressions.

The lens came back from the optician on the fourteenth of March, and I set it in the tube that evening to test against the tower clock. What I had ordered was a simple thing - a disc of crown glass ground to bring the meridian to a point - and what I received was a disc that showed me the weather on the glass itself, a faint blooming at the edge that I took at first for a defect in the grinding. Three nights I adjusted the focus and three nights I blamed the mounting. On the fourth I turned the lens in its cell, and the bloom travelled with the glass, which told me the fault was mine and not the instrument’s: I had been reading the sky through a film I had put there myself, with a cloth I had used to wipe the tube and had not thought to set aside.

The apprentice’s error is not that he cannot see. It is that he has already decided what he is looking at, and the glass is faithful to the decision.

What I would tell the person who finds this entry: the correction is small and it is the whole of the matter. I had believed the difficulty of learning to observe lay in the eye - in training it to hold steady, to wait, to distinguish the satellite from the star. I now believe the difficulty lies in the hand that wipes the lens, and in the assumption, so quiet it never announces itself, that the instrument is the thing that needs cleaning.