236 PHYSICAL GEOGRAPHY. 



applied to the east branch of the Pemigewasset. But the name of Pemi- 

 gewasset is preserved as a synonym, as it should be. The stream coming 

 down from Franconia is called the Middle Branch. 



The roads are laid down well in accordance with the old method of 

 presenting the general course, without reference to their minor irregu- 

 larities. 



Prof. Woodman's Report. 



In 1853 the governor was directed to "appoint a commissioner to 

 obtain the necessary information, and make estimates of the expense of 

 constructing a new and accurate map of the state." In his report the 

 following year, Prof. John S. Woodman, the commissioner, answers four 

 questions, viz., — What data, information, or facts are already within reach 

 for the construction of a new map .' What are necessary yet to be obtained 

 for a new and accurate map by actual operations in the field ? What is the 

 time and expense necessary for obtaining all that is required, and con- 

 structing a map ? What is the expense of engraving, printing, and manu- 

 facturing.' The answer he gives to the second question expresses well 

 the character of work required for the construction of a good map, and 

 the deficiency of Carrigain's map in this respect. 



An accurate map of a state is now understood to imply a map constructed upon data 

 obtained by a series of geodetic and astronomical observations, carefully conducted 

 with suitable instruments of the kind now in use for such work. Both instruments 

 and methods have been greatly improved within fifty years, so that a degree of preci- 

 sion is now easily attained which was formerly impossible. The general method is 

 briefly this : A base line of four to ten miles in length is accurately measured, and 

 from this a series of large triangles is supposed to cover the state like a net. The 

 sides of these triangles should be from twenty to forty miles long. The vertices of 

 these triangles are accurately determined in position and elevation by the observations. 

 Then a series of smaller triangles are taken so as to fix one or two points in or near 

 such town. Then the town maps are accurately made and put in their true position by 

 reference to the points determined by the triangulation. All the Coast Survey work in 

 New Hampshire is so much work done, with the requisite care, and the distance 

 between any two of these points can be used for a base, and the work readily continued 

 over the state from the points in this state and on the adjacent borders of Maine and 

 Massachusetts already established. The measuring of a base line with the required 

 accuracy is always expensive, and would be particulariy so in New Hampshire. The 

 work of the Coast Survey that could be used without expense would probably diminish 



