PORTABLE BAROMETER. 



TABLE. 



Inch 10th 



20 . 05 

 . 20 

 . 35 

 . 50 

 . 6"6" 

 . 82 



21 . 00 

 . 18 

 . 35 

 , 53 

 . 70 

 . 87 



^22 . 65 



. 25 



. 45 



. 65 



. 85 



Feet 

 130 

 129 

 128 

 127 

 126 

 125 

 124 

 123 

 122 

 121 

 120 

 119 

 118 

 117 

 lib' 

 115 

 114 



Inch 



10th 



Feet 



23 



. 05 



113 





. 25 



112 





. 45 



111 





. 65 



no 





. 87 



109 



24 



. 10 



108 





. 32 



107 





. 55 



106' 





. 30 



105 



25 



. 05 



104 





. 30 



103 





. 55 



102 





, SO 



101 



26 



. 05 



100 





. 30 



99 





. 57 



98 





. 85 



97 



Inch lOth 

 27 . 15 

 . 45 

 . 75 

 25 . 05 

 . 35 

 . 65 

 • 95 

 27 

 6" I 

 95 

 30 

 . 65 



31 . 00 

 . 37 

 . 75 



32 , 10 



29 



30 



Feet 



96 



95 



94 



93 



9^ 



91 



90 



89 



88 

 87 

 8(>* 

 85 

 84 

 83 

 82 

 81 



The method of using it is as follows : 1st. Add the two Method of 

 observed heights of the barometer, and halve the sum to ob- "^'"° e a ti. 

 tain the mean height. 2d. Subtract the lesser height from the 

 greater, the remainder is, of course, the difference in tenths, 

 &c. of an inch, 3d. Enter the table with the mean height, 

 and take out the feet answering to it, making a proportion if 

 the mean height does not exactly answer to a foot. (This pro- 

 portion may be made by head.) Multiply thenuniber thus ob- 

 tained by the tenths, &c. .of an inch of difference of height. 

 The result will be nearly the number of feet answering to the 

 difference of height bct^.veen the two barometers at the tempe- j^^ de^'-ee of 

 rature of freezing. When the lower barometer stands between accuracj', 

 29 and 30 inches, and the elevation does not exceed 1500 

 feet, this rule will give the height within one foot of the result 

 from the logarithmic method. When the elevation is abouf 

 3000 feet, the error v.ill be nearly three feet, and at heights 

 greater than 3000 feet the error increases in an higher ratio. 

 It is always in defect. In this country, however, such eleva- 

 tions do not exist, and in those parts where a knowledge of the 

 comparative heights of the different hills is the most generally 

 useful, they seldom exceed 1000 feet. At all events such ob- 

 servations 



