On the Height of Mountains, Headlands, fyc. 



13 



constant number .92102 ; this sum will be the logarithm of the 

 required height in fathoms. 



Obs. — The first four figures of the logarithms of the heights 

 of the barometer, together with the indices, are to be counted 

 whole numbers, and the numbers taken from Tables I and II 

 must always have five places of decimals, though they need not 

 always be used. 



Tables I and II may be dispensed with, as 456789 answers to 

 a degree of the attached thermometer in Table I, and 0024680 

 to a degree of the detached in Table II. 



Table I. 

 Of the allowance for the difference 

 of the temperatures of the attach- 

 ed thermometer. 



Table II. 

 Of the allowances for the mean tem- 

 peratures of the detached thermo- 

 meters. 



Previous to M. De Luc commencing his experiments on the 

 barometer, it was taught that a mean between the two tempera- 

 tures shown by the thermometer attached and the height of the 

 mercury in the barometer at two different stations, was sufficient 

 to determine the perpendicular distance of those stations. But 

 De Luc found by repeated experiments that an additional or de- 

 tached thermometer was likewise necessary, which has since 

 been confirmed by General Roy, Sir G. Shuckburgh, and others. 

 However, before making further remarks, we shall illustrate the 

 rule and tables just given by practical examples. 



Examples. 



I. The heights of the barometer at the bottom and top of a hill 

 are 29.862 and 26.137 inches; the attached thermometer at the 

 bottom and top indicates 68° and 63° ; also, the detached ther- 



