TRANSACTIONS OF SECTION J. 503 



8. On the Constmction of Hypsometrical Tables. 



By C. W. Adams, Chief Surveyor of Otago. 



The object of this paper is to facihtate the calculation of 

 heights from observations taken with an aneroid barometer. 



Most of the tables in common use adopt a fixed barometric 

 constant, requiring a tedious correction for every variation in 

 temperature. They are also framed on the erroneous assump- 

 tion that moist air has a constant coefficient of expansion — 

 viz., ^i-Q for each degree Fahrenheit. 



It is well known that air at a low temperature is much 

 nearer saturation than it is at a high temperature, say about 

 75 to 80 per cent, at 32°, and 50 to 60 per cent, at 80° Fahr. ; 

 and this variation in the hygrometric state of the air should be 

 taken into account in any formula for the calculation of 

 heights. 



So far as the author is aware, Mr. Arthur Beverly, of Dun- 

 edin, is the first mathematician who has attempted to construct 

 barometrical tables on this assumption, and his tables are un- 

 doubtedly a great improvement on all other tables previously 

 used. His object in w^riting this paper is to go a step further 

 still — viz., to advocate the construction of a special table for 

 each variation of climate. 



The author has constructed such a table for Otago, New Zea- 

 land, from data giving the hygrometric state of the air for all ordi- 

 nary temperatures recorded twice a day for a period of three 

 years, which, he states, is reduced to the utmost simplicity. The 

 corrections for temperature, and for the average hygrometric 

 state of the air at different temperatures, are provided for in the 

 table ; so all that is required is to take out the tabular number 

 corresponding to the sum of the temperatures, and one small 

 multiplication gives the resulting height (as he maintains) with 

 greater accuracy, and with less labour, than any of the tables 

 at present in use. 



