Optical Square Rangefinder c.1905 R. H. Stocken thanks largely to their Canadian

thanks largely to their Canadian instructors

Steward advert at the rear

almost two miles from where the mine exploded

There are no makers marks

GALE AND POLDEN LTD

Optical Square Rangefinder c.1905 R. H. Stocken thanks largely to their CanadianAn Optical Square rangefinder, dating from c. 1905, complete with its original fitted leather case. Reputed to have been invented by George Adams Senior in the middle of the 18th century, the optical square appeared in the 1795 catalogue of George Adams Junior as 'A small instrument for surveying by right angles'. In the 1907 Negretti & Zambra catalogue it was described as being used 'for fixing a right angle, and in the laying off of offsets'. A