VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. 147 



T., I have, for some time past, had my thoughts bent towards measuring, with 

 all possible accuracy, a base line. This base line, could I have chosen its situa- 

 tion, should have been determined as near the middle of the line of coast I am 

 surveying as possible; but circumstances have not permitted me to make unre- 

 strained choice of its place. On my arrival at Cuddalore, I was told that, as 

 I proceeded southward, I should meet with frequent rivers, and other water 

 courses, that would certainly obstruct me in the design I had formed of mea- 

 suring it on the sea beach, farther south ; and soon after my removal from that 

 place I found, with much satisfaction, that the coast between Cuddalore river 

 and Porto Novo would serve my purpose extremely well. The beach hereabouts 

 is flat, broad, and remarkably smooth; the only specious objection that can be 

 made to it, is its not being straight, but forming a curved line, concave towards 

 the sea. This however I knew to be, in reality, of no bad consequence, since 

 several right lines of sufficient length might, I perceived, be measured on it; 

 the angles they might interchangeably make, be taken; and the whole afterwards 

 be reduced to one direct line by calculation. 



Mr. T. measured the base with 2 rods of 25 feet long each. He had prepared 

 stands for placing them on ; but for some reasons dispensed with using them. 

 He therefore resolved to lay the rods, end to end, on the ground. It was in a 

 similar way that the base line for a series of triangles, continued throughout 

 France, was measured. Tlie French rods, which were nearly of the same length 

 and construction with mine, he says, were disposed, in the very same manner, 

 on the rugged pavement of a highway near Paris; so that I have every reason to 

 believe the opportunity here afforded, of a peculiarly level and sandy beach, to 

 be the best of the two. 



The mode of conducting the measurement was this: staves were first set up in 

 a direct line, between the flags; from every 2 of these staves a rope was occa- 

 sionally stretched, as tight as possible, on the ground, and the rods were laid by 

 the side of the rope. The first rod being properly placed, the 2d was laid near 

 its end, and then very carefully adjusted, so as to touch the ferrule of the other, 

 by a man, who had no other employment to engage his attention; and in the 

 performance of this office he was closely watched by myself. The ferrules, which 

 were of thick brass, had been rounded, not only to make the contact more visible, 

 but because the length of each rod was determined, by their having the spherical 

 figure, more easily. At the placing of every 2d rod, which was painted white to 

 distinguish it from the other, I registered its number myself in a book, ruled 

 purposely with columns, each column containing 10 numbers; my writer did the 

 same in another book: besides which, an attendant, who was furnished with JO 

 small sticks, gave the tindal, who also assisted in keeping the reckoning, one of 

 them every time the white rod was laid down; and each man made his separate 



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