Page:Philosophical Transactions - Volume 006.djvu/301

 Rh

SIR,

O perform my late promise to you, I shall without further ceremony acquaint you, that in the beginning of the Year 1666 (at which time I applyed myself to the grinding of Optick glasses of other figures than Spherical,) I procured me a Triangular glass-Prisme, to try therewith the celebrated phœnomena of Rh