1841.] Newman's improved Portable Barometer, ^c, 963 



It appears from the above, that the mean neutral reading for Portable Barometer, No. 

 40, viz. 23-313 is .043 of an inch too low, and in No. 44, the neutral reading 23-370 is 

 •Oil of an inch too higli. The following Examples will explain the method of reducing 

 the observed to the true readings for both instruments : — 



Example for Barometer, No. 40. 

 Suppose the observed reading on the scale to be 22-543 inches, the temperature of the 

 mercury being 49° Faht, — the true height of the column is required. 



Observed reading, h' = 22' -543 inches. 



Neutral do h = 23-313 



Difference, (h'— h) = —0-770 



Correction for capacity, i (h'— h) = —0-183 



Observed reading as above, h' = 22-543 



True height of column, H.= h' — - (h'— h) = 22-360 inches. 



Example for Barometer, No. 44. 

 Required the true height of the column of mercury, the observed reading on the scale 

 being 25-291 inches and the temperature of the mercury, 64° Faht. 



Observed reading, h' = 25-291 inches 



Neutral ditto, h. = 28-370 



Difference, (h'— h) = +1-921 



Correction for capacity, 1 (h'— h) = —-349 



Observed reading as above, .... h' = 25'29l 



True height of column, H. =h'+ i (h'— h) = 25 -640 



A correction would also be required for temperature, but with instruments of this 

 construction, i. e. as to relates to their scale, the reduction in this account is impracti- 

 cable. 



G r. 



