Review of[United States: Isogonic Charts for 1900]
Journal of Geophysical Research
In two official publications the same purpose--the construction of the isogonic char% for the United States, epoch I9oo--is carried out by two different departments of the United States Government. To which of the charts shall the outsider give preference? The first is constructed by a man hitherto unknown in the science of terrestrial magnetism; the second, .by one with nearly half a century of experience in this special field. .&gain, the first is issued from a department not engaged in the
... ot engaged in the making of magnetic observations, while the other comes from a department which for over fifty years has been actively engaged in magnetic work, and which is intrusted with the carrying out of the magnetic survey of the United States. With this statement of the facts we pass over to a critical examination of each publication. Geological Survey 2•ublicalion. Mr. Gannett states that this document "is designed to meet the needs of those who have occasion to use the needle in surveying, or who have to deal with surveys which have been run by needle in past times." This is the identical purpose of the magnetic work of the Coast and Geodetic Survey. In no other country has such a thorough study been made of the secular variation as that by Mr. Sehott for the United States. Mr. Gannett must, therefore, base his secular variation data chiefly upon the Coast Survey investigations The principal reason apparent to an outsider for Mr. Gannell's work would be the fact that his isogonic chart is based upon about ee,ooo declination results, while Mr. Schott's is based upon only about 3,6oo. Mr. Gannett's additional data are obtained mostly from the surveys of the United States General Land Office. These, it is claimed, Mr. Schott has overlooked. This additional material. as Mr. Gannett acknowledges, must be very carefully sifted. It is obtained, not from 1 UNITED ST&TES GEOLOGICAL SURVEY. •';Z•tioe Z)eclinalion in H•e U•tited Slates, by Henry Gannett. Extract from Part I of the •7th Annual Report of the Survey, •895-96. Washington. •896. Pp. =o3-44o. Two plates and three figures. UNITED STXT]•S COXST AND (•EODETIC SURVEY. Dislributio• of t/ze 3•Fag'netic Declination in lhe United Stales for tlte Epoch, Jan•ary x, x9oo, by Charles .•. $ehott. App. x, Report for x896. Washington. x897. PP. x47-e35. Three plates.