256 PROCEEDINGS OP THE AMERICAN ACADEMY 



XIX. 



MOUNTAIN SURVEYING. 



By Professor E. C. Pickering. 



Kead, Jan. 11, 1876. 



The difficulties and expense of a topographical survey are always 

 very great ; and this is particularly the case in a mountainous country, 

 owing to the short horizontal interval between the contours, their irreg- 

 ularity, and the labor involved in reaching the more elevated portions. 

 The objections to the usual trigonometrical methods are, that the 

 theodolite, or transit, needed to measure the angles, is heavy, liable to 

 injury when carried over a rough country, and the time required to 

 measure each angle is considerable. The labor and cost of measuring 

 a base-line are also very great. Moreover, the accuracy attained is 

 much greater than is ordinarily needed ; since, as the land is commonly 

 of little value, there is no need of determining positions with more 

 accuracy than they can be shown on a map. If tlie tract of country 

 is large, a scale greater than looV^^' ^^ stto^cJ' ^^ rarely used; and, 

 owing to the unequal expansion and contraction of the paper, long 

 distances could not be measured with accuracy on such a map much 

 nearer than within fifty to one hundred metres. Another objection 

 to the trigonometrical method is, that the work must be carried oa 

 continuously from one base to the other ; and no positions can be deter- 

 mined except by connection with a base through a series of triangles. 

 If, however, the latitudes and longitudes of several points are ascer- 

 tained, each of them may be used as a centre from which the form of 

 the surrounding country may be detex*mined ; and an error in one will 

 in no way affect the position of the others. The problem proposed, 

 therefore, was to devise some instrument which should give approxi- 

 mately the distance and elevation of a mountain summit or other 

 object, and which at the same time should be light and not easily 

 injured. AVith such an instrument, an exploring party, whenever they 

 camped at a point commanding an extensive view, could, during the 



