1881, Sanitary and Statistical Report of the Surgeon-General of the Navy, volume 5, page 257:
An air-port, which is only 6 inches in diameter when closed, cannot be expected to afford sufficient light in an apartment even so small as those allowed to ward-room and steerage, whether for purposes of reading, writing, or the examination of patients and recruits. This fact and the forced resort to artificial light explain the cause of premature loss of vision which is so common among the officers in our service. The large rectangular air-ports seem to be the remedy indicated.
