MEASUREMENT OF A BASE. 319 



the sides. This sen'es to place the whole in its proper po- 

 sition with respect to the cardinal points. The next thing 

 to be done is to place the tract surveyed between the two 

 parallels of latitude on the artificial globe, corresponding to 

 those on the surface of the earth which they represent. 

 This is done by determining by astronomical observations 

 the latitudes of any two stations in the survey at a con- 

 siderable distance north and south from each other. "When 

 this is performed, and the magnitude of the celestial arc in 

 the heavens expressed in degrees is compared with the mea- 

 sured length of the terrestrial meridian between the parallels 

 passing through the stations, the length of a degree on the 

 earth's surface will be known. 



The position of the whole as to its distance from the 

 equator or pole will now be known ; but its distance east or 

 west from some known meridian, that is, its diiference of 

 longitude, remains to be determined. This must be found 

 by means taught in the doctrines of astronomy. 



Colonel Lambton, being in possession of some valuable ' 

 instruments, and in expectation of others from England, 

 which the India Company had with the most laudable libe- 

 rality given him permission to procure, began the survey by 

 measuring a base on the table-land of the Mysore covmtry, 

 near Bangalore : it was more than 100 miles from the sea, 

 and on this account unfavourable, because its elevation 

 above the level of the sea required to be found, and this 

 could only be done by corresponding observations of the 

 barometer made at the base and at Madras. However, ' 

 having provided an apparatus similar to that employed for a 

 like purpose in the British survey, he commenced his labour 

 on 14th October, 1800, and completed it on 10th December. 

 After making the necessary corrections for the expansion 

 and contractions of the chain by heat and cold during the 

 process, he found the true length of the base, at the tem- 

 perature of 62° and reduced to the level of the sea, to be 

 39,267.706 feet, or 7.4321 miles. By a series of subsequent 

 astronomical observations, the latitude of the south end of 

 the base was foimd to be 12° 54' 6". 



Colonel Lambton resumed his labour in the year 1802. 

 He had by this time received a most complete apparatus 

 from England : this enabled him to execute his views on 

 the scale originally proposed, which was the measurement 



