330 Mv Galbraith's Barometric Measurements of Heights. 



cases, the numbers corresponding to inches, tenths, hundredths, 

 and thousandths of an inch of the height of each barometer, 

 may be readily found by simple addition, of which the differ- 

 ence forms the approximate heiglit as shown in the examples, 

 p. 823, 324. 



A very extensive table of this kind has also been published 

 by Mr Thomas Jones, the eminent mathematical instrument- 

 maker, Charing Cross, London, extending from 15 to 31 inches 

 of the barometer, and giving every thousandth part of an inch. 

 To those who use Fahrenheit's Thermometer, our Tables II. 

 III. Part I. may be convenient, as the tables given by Mr Jones 

 are adapted to the centesimal thermometer alone, both for reduc- 

 ing the mercury in the barometers to the same temperature, and 

 for making allowance for expansion of the air by heat. 



Table II. The second table is computed from the formula 

 (11.) adapted to a mean state of the atmosphere, and properly 

 varies according to the sum of the detached thermometers ; but 

 as the variation from this cause is small, it need hardly be at- 

 tended to, unless very great precision be required. There are 

 two parts, one adapted to Fahrenheit's scale, the other to the cen- 

 tesimal scale, so that cither may be used as required. 



As the method of computing the correction for the difference 

 of the mean temperature of the air from that of the freezing point 

 is somewhat troublesome, especially if Fahrenheit's thermometer 

 be used, 



Table III. has been computed to facilitate this process, and 

 the value" was derived from formula (7). 



It may be remarked, that this table is now engraved on Mr 

 Adie's sympiesometer, for the purpose of saving trouble, as the 

 only arithmetical calculation now required is the multiplication 

 of the difference of the numbers found from the sliding-scale 

 adapted to that useful instrument, by this factor, to give the 

 final result. 



Table IV. gives the necessary allowance for the change of 

 gravity, depending upon the latitude of the place of observa- 

 tion, and the height of the elevation measured. 



Table V. gives the Liorrection for the elevation of the lower 

 barometer above the sea, when the height of the upper above 

 the lower is 10,000 feet, and consequently that for any other 

 number different from 10,000 by taking proportional parts. It 



