248 LIGHT SCIENCE FOR LEISURE HOURS. 



may form some idea of the energy with which the survey 

 is in progress from the fact that Colonel Thuillier's 

 Report for the season 1866-67 announces the charting 

 of an area half as large as Scotland, and the prepara- 

 tory triangulation of an additional area nearly half as 

 large as England. 



In a period of thirty years, with but few surveying 

 parties at first, and a slow increase in their number, an 

 area of 160,000 square miles has been completed and 

 mapped by the topographical department. The revenue 

 surveyors have also supplied good maps (on a similar 

 scale) of 364,000 square miles of country during the 

 twenty years ending in 1866. Combining these results, 

 we have an area of 524,000 square miles, or upwards of 

 four times that of Great Britain and Ireland. For all 

 this enormous area the surveyors have the records in a 

 methodical and systematic form, fit for incorporation in 

 the atlas of India. Nor does this estimate include the 

 older revenue surveys of the north-western provinces, 

 which, for want of proper supervision in former years, 

 were never regularly reduced. The records of these 

 surveys were destroyed in the Mutiny chiefly in 

 Hazaumbaugh and the south-western frontier agency. 

 The whole of these districts remain to be gone over in 

 a style very superior to that of the last survey. 



The extent of the country which has been charted 

 may lead to the impression that the survey is little more 

 than a hasty reconnaissance. This, however, is very far 

 indeed from being the case. The preliminary triangu- 

 lation, which is the basis of the topographical survey, is 



