PLSO Oregon Surveyor July/August 2020

20 The Oregon Surveyor  | Vol. 43, No. 4 Featured Article Surveyors in the News Is your compass working properly? By Pat Gaylord, PLS Published in “The West Shore” newspaper in April of 1878 this article outlines variations that were found in compasses of the time. Do you own a historic compass? Are you sure it’s accurate? Read on. The West Shore Newspaper Portland, Oregon April 1878 Errors in Using Surveyors’ Compasses —A correspondent of The Engineering and Mining Journal mentions some mi- nor sources of error in taking readings from the compass while surveying. After noticing certain inexplicable vagaries of a compass needle, and testing the metal of the instrument, and afterward examin- ing the observer’s pockets to determine whether anything of iron or steel was on his person, the cause of the variations was discovered in the frame of the mag- nifying glass. The frame was of vulcanite, or hard rubber, polished to a high gloss; this frame was liable to become electri- fied by the slightest friction, such as is caused by carrying in the pocket. Further investigation showed that from a variety of similar causes, all ordinary frames of magnifiers are apt to give like trouble, and new ones had to be specially made which were free from the defect. The impure metal of cases, rivets and oth- er parts may give rise to this attraction; an iron ring is sometimes inserted to fix the glass in the frame. Sometimes the observer may unconsciously carry the iron in his hat, in the wire that stiffens the brim. Aluminum, especially when hammered, has the polarizing property. Finally, there is a story of a land surveyor who had the appearance of his compass improved by nickel plating, which was applied to almost the entire instrument —ball, socket and sights—the effect of the needle being the same as if the brass had been coated with iron.  x