The "prize" concerning which you write is a medal, awarded as you correctly state, "for important discoveries connected with heat or light". The discovery should be embodied in a manuscript and endorsed by some Fellow of the Royal Society as suitable to be brought forward. It is not at all necessary for the discoverer himself to be a Fellow of the Society. Inclosed herewith I send you the circular stating the qualifications for Fellowship.
I am, your obedient servant,
Asst. Sec. R.S. [Assistant Secretary, Royal Society]'.