The Mapping of the Earth. 567 
less reliable according to the skill of the explorer and the time and 
opportunities at his disposal. 
In recent years considerable improvement has been made in the 
instruments and methods of the geographical surveyor: the introduc- 
tion of the Invar tape for the measuring of the baselines, the more 
general application of triangulation, the substitution of the theodolite 
for the sextant, the use of the plane-table for filling in the topo- 
graphical details of the survey, the application of wireless telegraphy 
to the determination of longitudes, these and other improvements 
have all tended to greater accuracy and efficiency in geographical 
and topographical mapping, so that in many respects the rough 
approximate methods of the earlier explorers are fast being super- 
seded by instruments and methods more in keeping with modern 
requirements in map-making. 
Still, the principle underlying all surveying is the same, and the 
whole subject really amounts to the best and most accurate methods 
of measurement with a view to representing on a plane, on a greatly 
reduced scale, the leading features of a certain area of the earth’s 
surface in their relatively correct positions; and so it resolves itself 
into geometrical problems of similar angles and _ proportional 
distances. This being the case, it is clear that it becomes in the 
main a question of correct angular and linear measurements, and all 
the improvements in survey methods have had for their object the 
increased accuracy of accomplishing this, together with greater 
facility for computing the results. . . . 
So far what I have said has had chiefly to do with some of the 
earlier attempts at surveying and map-making, and the instruments 
and methods by which these have been carried out; and I will now 
try to give you an outline of what has been done in comparatively 
recent times, and state briefly the present position of various parts of 
the world as regards the condition of their mapping and the survey 
basis upon which their maps depend. 
Little by little civilized man, by his daring, his love of adventure, 
and the necessities of events and circumstances, has penetrated into 
the unexplored parts of the earth and pushed back the clouds and 
mists that so long shrouded them from his knowledge, until at the 
present time the regions that are entirely unmapped are very few 
indeed, and do not amount to more than about one-seventh of the 
whole land-surface of the globe, including the unexplored areas of 
the Polar regions, which may be either land or water. Not content 
with a mere vague acquaintance, he has striven for greater accuracy, 
and has turned to various branches of science and called them to his 
aid, in order that he may obtain more correct knowledge and a better 
comprehension of the earth’s features. To enable him to fix with 
definiteness the position of places upon its surface, map out the 
various land-forms, and obtain their accurate measurements, he has 
consulted the astronomer and mathematician. Commencing, as we 
have seen, with the rudest instruments and measuring apparatus, 
these, as greater accuracy was required, have gradually been 
improved, until the present-day appliances and equipment of 
a surveyor are a wonder of refinement and delicacy. 
