Draft letter, from Sir John Herschel to William Radcliffe Birt, dated at 28 A Devonshire St., Portland Place Autographed draft letter, signed or initialed by sender. How to reduce barometer observations and project them in curves. Royal Society [of London] will provide table by H. C. Schumacher for this purpose. How to obtain 'law of decimal oscillations' for each station. William Radcliffe Birt's name will be affixed to results. John Frederick William Herschel needs receipt for observations, which belong to South African Literary and Philosophical Society. 22 May 1840