|Description||The drawing was sent from Monsieur Thevenot in Paris to Henry Oldenburg. It is part of an English letter in the hand of Henry Oldenburg, which must be his English translation of the original French. |
It explains how the instrument can be made, and also how it should be used. The instrument was used to measure refractions coming from a pool of water and consists of a triangular glass.
Subject: Optics / Astronomy