(j£ MEASUREMENT OP HEIGHTS BY THE BAROMETER. 



give the result by mere inspection : but unless tliey should 

 be continued to every hundredth of an inch (in which case 

 they would make a volume) the trouble of subtraction is 

 all that would be saved. 



Table 3. Gives the correction for the expansion of air 

 for every 1000 feet of altitude. It is calculated for every 

 degree of the mean temperature from 72 to 32. It is pro- 

 bable that few observations will be made in this island, 

 where the mean temperature is not within these limits. 



This table is calculated from Table 5, p. 484, of Gregory's 

 Mechanics, vol. 1. 



With regard to the correction for the expansion of the 

 mercury, it may be obtained without any sensible errour, 

 by multiplying the difference of temperature in degrees of 

 Fahrenheit by 275 feet, or 2 feet 9 inches. 



Yours, &c. 



J. B. 



Ear. 



TABLE I. 



B. F. 



TABLE II. 



B. 



25*0 



5606 



27*0 



3600 



29-0 



1738 



•1 



5502 



•1 



3504 



•1 



1648 



•2 



5398 



*2 



3408 



•2 



1559 



•3 



5295 



•3 



3313 



•3 



1470 



•4 



5192 



•4 



3217 



•4 



1381 



•5 



5090 



•5 



3122 



•5 



1293 



•6 



4988 



•6 



3028 



•6 



1205 



•7 



4886 



•7 



2934 



•7 



1117 



•8 



4785 



•8 



2840 



•8 



1029 



•9 



4684 



•9 



2746 



•9 



942 



26-0 



4584 



28*0 



2653 



30-0 



855 



•1 



4483 



•1 



2559 



•1 



768 



•2 



4384 



*2 



2467 



•2 



681 



•3 



4285 



•3 



2375 



•3 



595 



•4 



4186 



•4 



2283 



•4 



509 



•5 



4087 



*5 



2191 



•5 



424 



•6 



3989 



•6 



2100 



•6 



338 



•7 



3891 



•7 



2009 



•7 



-253 



•8 



3794 



'8 



1918 



•8 



169 



•9 



3697 



28'9 



1828 



•9 



84 



25-0 



10-4 



•0 



—•3 



•5 



—•2 



•7 



—•1 



26-0 



—•0 



•3 



-9'9 



•5 



—•8 



•8 



—•7 



27'1 



—•6 



•3 



—•5 



•6 



—•4 



•9 



—•3 



28-2 



—•2 



•5 



— -1 



•9 



—•0 



29-2 



-8-9 



•5 



—•8 



•9 



—•7 



30-2 



—•6 



•6 



—•5 



31-0 



—•4 



TABLE 



