In reply to your letter of the 11th April, there has been no Secretary of the Royal Society of the name you mention. On April 2nd, 1835, however, John David Roberton became the Assistant Secretary to the Society, so perhaps this is the gentleman referred to.
I am, Dear Sir, faithfully yours,
Robt [Robert] Harrison
Asst. Sec. R.S. [Assistant Secretary, Royal Society]'.