▁change ▁in ▁magnetic ▁variation . ▁ ▁In ▁ 1 6 3 7 , ▁using ▁a ▁spe cially ▁built ▁astronom ical ▁se xt ant ▁with ▁a ▁ 5 - foot ▁radius , ▁Richard ▁Nor wood ▁measured ▁the ▁length ▁of ▁a ▁na ut ical ▁mile ▁with ▁ch ains . ▁ ▁His ▁definition ▁of ▁ 2 , 0 4 0 ▁yards ▁is ▁fairly ▁close ▁to ▁the ▁modern ▁International ▁System ▁of ▁Units ▁( SI ) ▁definition ▁of ▁ 2 , 0 2 5 . 3 7 2 ▁yards . ▁ ▁Nor wood ▁is ▁also ▁cred ited ▁with ▁the ▁discovery ▁of ▁magnetic ▁dip ▁ 5 9 ▁years ▁earlier , ▁in ▁ 1 5 7 6 . ▁ ▁Modern ▁times ▁ ▁In ▁ 1 7 1 4 ▁the ▁British ▁Commission ers ▁for ▁the ▁discovery ▁of ▁longitude ▁at ▁sea ▁came ▁into ▁prom in ence . ▁ ▁This ▁group , ▁which ▁existed ▁until ▁ 1 8 2 8 , ▁offered ▁gr ants ▁and ▁re wards ▁for ▁the ▁solution ▁of ▁navig ational ▁problems . ▁ ▁Between ▁ 1 7 3 7 ▁and ▁ 1 8 2 8 , ▁the ▁commission ers ▁dis b urs ed ▁some ▁£ 1 0 1 , 0 0 0 . ▁ ▁The ▁government ▁of ▁the ▁United ▁Kingdom ▁also ▁offered ▁significant ▁re wards ▁for ▁navig ational ▁accomplish ments ▁in ▁this ▁era , ▁such ▁as ▁£ 2 0 , 0 0 0 ▁for ▁the ▁discovery ▁of ▁the ▁North west ▁Pass age ▁and ▁£ 5 , 0 0 0 ▁for ▁the ▁navig ator ▁that ▁could ▁sail ▁within ▁a ▁degree ▁of