CLARKE, ALEXANDER ROSS British geodesist, was born in Sutherlandshire on Dec. 16, 1828. He studied at the Royal Military academy, Woolwich, and in 1847 became a second-lieutenant in the Royal Engineers. In 185o Clarke was posted to the Ordnance Survey at Southampton, and except for a break between 1851-54 he remained there until he retired in 1881.
When Clarke joined the Ordnance Survey the observations on the Principal Triangulation had just been completed, and he had the task of reducing and publishing the results. This was done in record time, and in 1858 appeared Account of the Observations and Calculations of the Figure, Dimensions and Mean Specific Gravity of the Earth as Derived Therefrom. Clarke was mainly responsible for a good deal of similar work carried out in co operation with other countries. His work was remarkably accurate and rapid, considering the laborious methods of calculation and reduction in use at the time. In a specially-designed room he tested and compared the standards of length used by other coun tries and by the Colonies, publishing his observations in Com parison of the Standards of Length of England, France, Belgium, Prussia, India and Australia (1866).
Clarke gave an account of the observations which connected the English and French triangulations under the title of Extension of the Triangulation of Great Britain into France and Belgium (1863) . He was the author of Abstracts of Spirit Levelling in England, Wales and Scotland 0860, Geodesy (188o) , a standard work on this subject, which has been translated into many lan guages, and a number of papers in scientific journals. He was a member of many learned societies and was awarded the Royal Medal of the Royal Society in 1887. He had been made a Com panion of the Bath in 18 7o. In 188 i Clarke was ordered to hold himself ready for service in Mauritius and preferred to retire rather than sever his connection with the Ordnance Survey. He lived a secluded life until he died on Feb. 11, 1914.