Autograph Letter Signed, agreeing to give a lecture entltled “The Chief Astronomical Observatories of the World”. 1 page 8 x 5 inches, in good condition. 63 Eaton Rise, Ealing, 23 September 1891. Andrew Ainslie Common FRS (1841 – 1903), English amateur astronomer, best known for his pioneering work in astrophotography. In 1876 Common became a Fellow of the Royal Astronomical Society. About this time he also moved to Ealing outside London where he would live for the rest of his life operating an astronomical observatory from the back garden of his house. Common realized he would need very large telescopes to gather enough light to record the images of stars photographically so he began building a series of ever larger Newtonian reflecting telescopes using the then new technology of silver coated glass mirrors. Dr. Common was largely retired by 1890 and devoted himself full-time to optical design and construction until his death. Most of his time was spent in the design of telescopic and optical sights for the Royal Navy and the Royal Artillery, in which work he was a pioneer. Captain (later Admiral Sir) Percy Scott, one of the leading gunnery officers of the Royal Navy, stated in 1902 that Dr. Common had “…produced (that is “designed”) a telescope sight which would, when properly used, quadruple the fighting efficiency of our battleships.” In response problems of rifle aiming and accuracy revealed in the 2nd Anglo-Boer War, he designed an experimental short telescopic sight for the Lee Enfield rifle, on a removable offset mounting graduated up to 2000 yards range, which anticipated several features used on many later military rifle ‘scopes.