How large seems the Moon?

Abstract

READING Mr. R. A. Proctor's communication under the above heading in NATURE of March 3rd, reminds me of an experiment I tried some time ago. I imagined I should get all sorts of answers to the question, varying from “a fourpenny-piece” upwards, without any particular size being more frequently pitched on than any other. I did not collect more than about twenty or thirty replies, but they were sufficient to show that, contrary to my expectation, one to two feet was assigned more frequently than other sizes. Mr. Proctor says the estimate of a foot in diameter assigns a distance of 115 feet to the moon. If he were to try to convince the observer of the soundness of this deduction, the latter would probably meet him with vehement reiteration that he only means the moon looks a foot large. It seems to me fairer to say that such a man thinks a two-foot rule 115 feet off, a fit and proper measure for celestial objects. I think many, who are aware of the futility of attempting to convey their ideas to other minds by these comparisons, yet involuntarily make them in their own. I am conscious of a lurking idea that the moon is more like a fourpenny-piece in size than anything else. The question is, what is the cause of the “personal equation” which determines for each individual the distance of the imaginary two-foot rule—and why is about 115 feet more common than other distances?