THE TKOCiKKSS OF GE< KJRAl'HIOAL KNOWLEDGE. 8G7 



ill the field ot" f^coo-rapliy, iiowexor. is not contincd to the transfer 

 of news to easuiil travelers. It is the faeility whieli it plaees in the 

 hands of the geoo"ra})her for deterniininu- his position in lono-itudc that 

 renders it so important a factor in the proseention of a y'eoo-raphical 

 sui'vev. Everyone knows that tlu> tirst duty of a o-eooraplier is to 

 diseover his latitude and his longitude. Hitherto the deterinination 

 of the tirst has been a matter of no o-reat uncertainty, but as reg-ards 

 the latter one can only say that the contidcncc expressed by most 

 explorers in the results of their observations has nexer l)een justitied 

 by the tinal verdict of a su1)se([uent determination. It is, in truth, 

 most difficult even for the most practiced observer to ol)taiii an abso- 

 lute \alue in lon^•itud(^ on which he can rely within such limits of 

 accunicy as are essential to the construction of a ma]) where these 

 values have to be employed diU'erentially. The telegraph places in 

 our hands the means of ditierential determinations within a decree of 

 exactness that surpasses even that of the most careful determination 

 of latitude: and the telegraph is everywhere. Supplementary to the 

 facilities of time sig-naliug- by telegraph is the wonderful accuracy of 

 graduation introduced into the smaller classes of new instruments 

 which in these davs rei)lace the cumbersome eiiuipment of the past. 

 A\'ith a small O-inch theodolite fitted wdth a complete vertical circle, 

 time values can ])e determined within a fraction of a second and lati- 

 tude values to within two seconds of arc, always provided that that 

 great bugbear of the astronomical geographer, level deflection, does 

 not interfere with his results. But the same minute accuracy in 

 graduation which has so improved the ordinary little instruments 

 which you find in the hands of the professional g-cographer has, when 

 combined with new methods for accurate linear measurement, also 

 placed it in his power to carry out a fairly coheivnt and systematic 

 triangulation with great rapidity and accuracy over large areas of 

 country whenever the configuration and characteristics of that coun- 

 try are favorable. Usually they are favorable, Large ex})anses of 

 flat desert, of undulating ^■eldt, or of unbroken forest are the excep- 

 tion, not the rule, and they must of course be dealt with as their 

 special peculiarities demand; and for the normal conditions of land 

 configuration, given that tli(^ explorer is specially carc^ful about his 

 l)ase measurements and his initial data, he can certainly, with modern 

 instruments and the facilities for check given him by the telegraph, 

 carry on a rapid and comprehensive geographical survey which will 

 fulfill all the conditions required by the administrator, (M-onomist, 

 political geographer, or military commander within such limits of 

 accuracy as will insure its standing all the sul»se(|ueiit tests that 

 geodesy may apply without any apparent map dislocation. And 

 practically that is all that is wanted for a first ma[). I have used the 

 word " rapidly.'' Few people, even scientific geographers, have really 



