The Surney and Mai) ^f Massachusetts. 83 



plement it. This was done in part by the Coast and Geodetic 

 Survey and in part by the Geological Survey. By these several 

 agencies upwards of 500 points were made available for the use 

 of the topographers. These are in the main well distributed, fur- 

 nishing upon each sheet a sufficiency, while upon many the num- 

 ber is greatly in excess of the requirements. 



The work of location has been done in different parts of the 

 state by different methods as seemed most applicable to the dif- 

 fering conditions of relief, forest covering and culture. Through- 

 out most of the western part of the state the work was done 

 entii-ely with the plane table, using the method of intersections as 

 the means of location. Each plane table sheet comprised one- 

 half of an atlas sheet, cut along a parallel of latitude. The plane 

 tabler, starting with three or more locations upon his sheet, fur- 

 nished by the triangulation, expanded over the sheet a graphic 

 triangulation, locating thereby a considerable number of points, 

 before commencing detailed work. This was done as rapidly as 

 possible, consistent with a high degree of precision. The reason 

 for covering the sheet with the graphic triangulation beforehand 

 lay in the necessity for locating a considerable number of points 

 before the sheet had opportunity to become distorted by alter- 

 nations of moisture and drying. This done, the plane tabler 

 went on with his usual routine of work, locating minor points 

 and sketching the topography in contours. The map was as far 

 as possible completed upon the stations, with the country in view. 

 Elevations were determined as the work progressed, with the 

 vertical circle of the alidade, and minor differences of elevation 

 between points whose height was known were measured by 

 aneroid barometer. 



In this work several different forms of plane table have been 

 employed. It was commenced with the large heavy movement 

 designed I believe by the Coast and Geodetic Survey. This, 

 however, was found unnecessarily heavy and cumbersome, and it 

 was discovered that the requisite degree of stability could be 

 obtained with much less weight. For this plane table movement 

 there was soon substituted another form in use in the Coast and 

 Geodetic Survey, which is very much lighter. This was soon 

 improved by taking off the slow motion in azimuth, which was 

 found to be unnecessary, and the addition of more powerful 

 clamps, for the purposing of rendering it more stable. A still 

 more stable form, however, coupled with even less weight, was 



