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Now in regard to measures. I must begin with some ideas 

 upon the way in which extensive measures are made upon the 

 surface of the earth. I daresay there are gentlemen present who 

 are so well accustomed to the ordinary process of surveying that they 

 will enter into the matter at once ; but it appears proper to explain 

 to my audience the way of proceeding. In the first place a line 

 of a few miles in length, commonly six or eight miles, is measured 

 with the utmost care — with a degree of care of which you have no 

 conception — with bars brought into contact in the most definite 

 way, in which intervals are measured in the most exact manner, 

 with corrections for temperature, and many other things into which 

 I cannot enter at present. Surveyors will easily comprehend that 

 if a theodolite is placed at each end of this base-line, and if an 

 object on a hill is observed at a distance, there is no difficulty in 

 ascertaining the distance of that new point on the hill from either 

 of the ends of the base. Then advantage of that determination is 

 taken to go to another hill, and then to two or three more hills ; 

 and hill after hill is observed in that way till by these processes a 

 whole country is covered by triangulation. It is possible to lay 

 down a map of a large district in which the distance between any 

 one point and any other point is certain perhaps within a few inches. 

 I have here two specimens of this triangulation. I am sorry that 

 the nature of the address does not admit of exhibiting them in a 

 manner in which they can be seen by a large audience like this, 

 but as I propose to stay here at the conclusion as long as it may 

 appear advantageous, I shall be glad if gentlemen taking interest 

 in the matter will come upon the platform and look at these. This 

 (pointing to a map) is one of them. This is the triangulation over 

 the greater part of Europe, as it existed a few years ago. Then 

 (pointing to a second map) there is another. This is the triangu- 

 lation of the great survey of India, which is one of the most 

 remarkable triangulations in the world. I hope those who have 

 followed me in the principle of triangulation will inspect these two; 

 they are authentic documents, and you will learn something from 

 them. That is the first process in the way of measuring upon the 

 earth, Now arises the question — how is this to be made available 



