312 MEASURE OF A DEGREE ON THE COROMANDEL COAST. 



in the centre, for supporting the coffers, making no other 

 use of pickets than for the drawing and weight posts, and 

 for carrying the register heads. The top of each stand or 

 tripod was a thick circular piece of wood, fixed firmly to the 

 end of the elevating screw, and a slip of board was fastened 

 across the circular top, screwed into the centre, and allowed 

 to turn round. When the ends of two coffers were placed 

 on the top piece, this slip of board was admitted into the 

 under part of each, and prevented their sliding off, a 

 precaution that was very necessary on account of the high 

 winds. 



Commence- The point of commencement of the base was had by drop- 



ment of the ping a plummet from the arrow of the chain suspended by 

 a silken thread. A long but small bamboo picket had been 

 driven into the ground, till its top was level with the sur- 

 face, and the cavity of the bamboo was such as just to re- 

 ceive the plummet, and when the first chain was in the cof- 

 fers, drawn out; by the weight at the opposite end, it was 

 adjusted by the finger screw at the drawing post in such a 

 manner, that the plummet might hang suspended over the 

 cavity of the bamboo, while the thread was applied to the 

 arrow. This was done within the observatory tent, that the 

 plumb line might hang freely without being disturbed by 

 the wind. The bamboo picket was preserved with great care 

 during the time I was observing for 'the latitude, and was 

 then protected under the frame of the zenith sector. When 

 the tent was removed, a large bamboo flag-staff was erected, 

 the cavity of which covered the picket, and in this state it re- 

 mained until the measurement was completed. 



Termination of At the termination of the base, being the end of a chain, 

 one of the large hooped pickets was driven into the ground 

 till its top was on a level with the cofFers and under the ar- 

 row of the chain. The opposite end being adjusted by the 

 finger screw, the arrow at the leading end was nearly the 

 centre of the picket. A mark was made, and a small round 

 headed nail was driven in till it was level with the surface. 

 The chain was again applied, and the arrow cut the centre 

 of the nail. I he picket had been driven upwards of two feet 

 and a half into very hard clay. 



The extremi- But that these extremities may be preserved, in case they 



i *»>' 



