270 LIGHT SCIENCE FOR LEISURE HOURS. 



vejors. But to complete in this style the survey of the 

 whole of India would be the work of several centuries. 

 The trigonometrical survey of Great Britain and Ire- 

 land has been already more than a century in progress, 

 and is still unfinished. It can, therefore, be imagined 

 that the survey of India nearly ten times the size of 

 the British Isles, and presenting difficulties a hundred- 

 fold greater than those which the surveyor in England 

 has to encounter is not a work which can be quickly 

 completed. 



But the growing demands of the public service have 

 rendered *it imperatively necessary that India should 

 be rapidly and completely surveyed. This necessity 

 led to the commencement of the Topographical Survey 

 of India, a work which has been pushed forward at a 

 surprising rate during the past few years. Our readers 

 may form some idea of the energy with which the sur- 

 vey is in progress from the fact that Colonel Thuillier's 

 Report for the season 1866-'6T 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 



