TERRESTRIAL REFRACTION. 5 



its extremities above the other, (ascertained in the 

 course of the measurement) afforded every necessary 

 datum to proceed on in this investigation. 



As the detailed account of the abovementioned 

 operation will appear at full length in Major Lamb- 

 ton's reports, and cannot with propriety be given in 

 this paper, I hope that its being known to form a 

 part of the trigonometrical operations, carried on in 

 the peninsula of Lidia, will appear a sufficient pledge 

 of its accuracy. 



ACCOUNT OF INSTRUMENTS. 



The elevations and depressions were taken with 

 the great theodolite, used by Major Lambton, for 

 carrying on his series of primary triangles across the 

 peninsula. This instrument, having been formerly 

 described by himself, need not be any further parti- 

 cularised. The angles were invariably taken with 

 the micrometer in the focus of the telescope. 



A barometer and thermometer were also procured*; 

 but from the reasons above given, the want of an 

 hygrometer was likely to deprive me of what I 

 considered to be an essential means of investiga- 

 tion (though I cannot find that such an instru- 

 ment was ever applied to a similar purpose) when 

 Lieutenant Kater, of H. M. 12th regiment, com- 

 municated to me his observation, on the bearded 

 seeds of a wild grass, called in the Malabar tongue 

 Panimooloo (the Andropogon contortum of Linn/Eus) 

 which grows in abundance in this part of the penin- 

 sula, and which he thought was likely to answer for 

 an instrument of this sorff. 



* The barometer was a common one, the property of Dr. IJeyne, 

 the company's naturahst. The thermometer, one of Fahrenheit's 

 division. 



t The beards of the wild oats have been used in England for a 

 similar purpose (see Hutton's Dictionary, art. Hygrometer), 



B $ 



