596 



THE HEIGHT OF THE WORCESTERSHIRE BEACON, 

 ABOVE THE LIBRARY, GREAT MALVERN, 



Deduced hy the formulcB of Maskelyne^ Hutton, and Daniell, from two 

 distinct Barometrical Measurements ; 



BY W. ADDISON, F. L. S., . 



SURGEON TO HER ROYAL HIGHNESS THE DUCHESS OF KENT, MALVERN. 



The barometric measurement of hills or mountains is an operation 

 of great nicety, and the results can only be considered as very 

 rough approximations, unless all the corrections for the moisture 

 and temperature of the air are duly attended to. Ever since the 

 celebrated and important experiment of Torricelli, the attention of 

 some of the greatest philosophers has been drawn in succession to 

 this interesting problem ; and the difficulty of estimating the 

 quantity and effects of aqueous vapour has hitherto been one of the 

 chief obstacles to the attainment of accuracy. Daniell's hygrome- 

 ter appears better calculated than any other instrument to remove 

 this obstacle. This Hygrometer was used in the measurement of 

 the height of the Worcestershire Beacon, which I am now about 

 to detail. 



Dr. Maskelyne's formula for determining the height of moun- 

 tains by the barometer is as follows : — 



1. Take the difference of the tabular logarithms of the observed 

 barometrical heights, at the two stations, considering the first four 

 figures (exclusive of the index) as whole numbers. 



2. Observe the difference of Fahrenheit's thermometer at the 

 two stations ; multiply this difference by 0.454, and add or subtract 

 this product according as the thermometer was highest at the 

 upper or lower station — which will give an approximate height. 



3. Take the mean between the two altitudes of the thermometer 

 and find the difference between this mean and 32°' Multiply the 

 approximate height by this difference, and the product by the 

 decimal fraction 0.00'^^44. This last correction being added to or 

 subtracted from the approximate height, according as the mean of 

 the two altitudes of Fahrenheit's thermometer was greater or less 

 than 32°, will give the true height of the upper station in English 

 fathoms. 



Dr Hutton's rules are as follows : — 



1. Let the heights of the barometer at the top and bo'tom of 

 any elevation be observed as near the same time as may be, as also 

 the temperatures of the attached thermom.ners, and the tempera- 

 ture of the air in the shade at both stations, by means of detached 

 thermometers. 



2. Reduce these altitudes of the barometer to the same tempera- 

 ture, by augiiicnting the height of the mercury in the coiaer 



