THE MOST CURIOUS CRAFT AFLOAT 



231 



DESERT SCEXKKY : IIELWAX, EGYPT 



Venezuela, West Indies, Bermuda, Af- 

 rica, Turkey, Asia Minor, Persia, Asiatic 

 Russia, China, and the South Pacific 

 Islands. It is, furthermore, cooperating 

 with various polar expeditions, and is 

 thus securing magnetic data in those far- 

 ofif regions. In another five years it is 

 confidently expected that the Carnegie 

 Institution of Washington will be able to 

 issue new sets of magnetic charts for 

 nearly the whole earth, as based for the 

 first time upon uniformly and systematic- 

 ally acquired data. 



Why was all this work needed, and 

 why is it that this country has now taken 

 the lead and has the good-will and the 

 effective cooperation of every civilized 

 country in the prosecution and comple- 

 tion of a project covering the entire 

 globe — "the magnetic survey of the 

 earth"? 



"the magnetic state of our globe is 



oxxe of swift axd ceaseless 



change" 



In the year 1634 Henry Gellibrand, 

 professor of mathematics at Gresham 

 College, found, upon careful observation, 

 that the compass pointed, at London. 4 

 degrees 6 minutes east of north. His 

 predecessor had observed, in 1622, not 

 quite 6 degrees, and Borough and Nor- 

 man, in 1580, had noted it ^4 degrees 

 east. Hence between 1580 and 1634 the 



easterly direction of the compass had 

 changed by 7 degrees. Before Gelli- 

 brand's time it had become generally 

 known that the compass changed its di- 

 rection from place to place over the 

 earth, but it was supposed "fixed and 

 invariable at any one place" ; but now 

 an entirely new fact became known. 



Since Gellibrand's time the fact that 

 the compass changes its direction with 

 time has become definitely known, and 

 has painfully impressed itself upon every 

 surveyor who has attempted to relocate 

 land bounds by the bearings recorded in 

 the original deeds of conveyance. He 

 must make due allowance for the 

 changes, and that is just where the trou- 

 ble comes in — the amount of change to 

 allow since the original survey. For the 

 same reason navigators' compass charts 

 are soon put out of date and so require 

 to be corrected. 



Sir John Herschel aptly said : 

 "The configuration of our globe — the 

 distribution of temperature in its inte- 

 rior — the tides and currents of the 

 ocean — the general course of the winds 

 and the affections of climate — whatever 

 slow changes may be induced in them by 

 those revolutions which geologv traces — 

 yet remain for thousands of vears appre- 

 ciably constant. * * * But the magnetic 

 state of our globe is one of swift and 

 ceaseless change. A few vears suffice to 



