428 , HOW MAPS ARE MADE. 



actual equipment: A 6-incli sextant, an aitificial liorizon, a pocket 

 cliiouonieter, a prismatic comi)ass, and a i)Ocket compass; two boiling- 

 point tliermometers and twocommon tbei monietersj aneroid barometer, 

 a Xdiitical Almanac, and a book of matliematica] tables, 



Tlie sextant, as we lia^ e seen, is for taking astronomical as Mell as 

 terrestrial angles; the thermometer and barometer for taking heights. 

 The principle on which the latter are calculated is the pressure of the 

 atmosphere. Tlie aneroid everybody knows; the boiling-point ther 

 mometer is considered better and more accurate, though 1 observe from 

 Livingstone's notes, who was the most painstaking and thorough ob- 

 server, and who always observed Avith both, that there was little prac- 

 tical dift'erence in the readings. Roughly sjteaking, water boils atsea- 

 level at 212oF., and the barometer stands at 30 inches, Avhile at 5,000 

 leet altitude water boils at 202'Go, and the barometer falls to 24-7 

 inches. 



The traveller in unexplored parts generally estimates his distances 

 from the time taken at the average rate of marching, just as on board 

 sliip <listances covered are roughly taken from the average rate of the 

 ship indicated by the log. He takes compass bearings as he goes, and 

 keeps an itinerary, recording all useful information gathered on the 

 march. He corrects Lis reckoning by taking daily latitudes, and at 

 greater intervals, say once a fortnight, longitudes from moon observa- 

 tions if he can. He notes heights, gets reports from natives of esti 

 mated distances, and in fact gathers all the information he can on every 

 subject — rain-fall, botany, zoology, antliropology, and so forth. Living- 

 stone did all these, and did them thoroughly. A whole lecture could 

 be written on these maps I hold in my hand. Here is one ot his notes: 



"Eight days uj) this river 90 miles, then cross and go three days, say 

 3G miles, to stone houses 132 miles — course southwest Lobula, comes to 

 northeast, has dark water." 



A traveller with his wits about him can do much with very rough 

 instruments, or even with none ar all. He can train himself to use his 

 fingers for rough angular measurements, and he can improvise in many 

 ways. My own old chief, the late Col. W. B. Holmes, E. E., used to 

 make wonderful surveys with his watch alone. 



One great geographical i)roblem — where does the huge river Sangpo, 

 which flows in Tibet at the back of the Himalaya , discliarge its waters ? — 

 was solved by a native surveyor, A. K., sent out by the Government of 

 India, who was obliged to conceal all his observations. I quote from 

 the ofticial account: 



"For linear measurement A. K. trusted entirely to his own pace or 

 step, which, as hereafter shown, is conveitible into the unit of a foot, 

 or any other unit desired; and notwithstanding that in Mongolia he was 

 looked down upon as a particularly inferior individual, because, unlike 

 the Mongols, he ])ersisted in walking instead of following the universal 

 custom of the country, which enjoins riding a horse on all i>ossible occa- 

 sions, he yet manfully strode along his travels, pleading poverty, or 



