194 Mr. De la Beche on M. Oltmanns' Tables for 



is very consistent with the dimensions of the spheroid deduced 

 from the meridional arcs. Now La Rogiere is only 1° 9' south 

 of the parallel on which the measurements have been made in 

 France and Italy ; and it is well known that the result of 

 these operations requires a compression considerably different 

 from what we have investigated. Here there is a difficulty 

 of some moment, which it would be interesting to discuss, but 

 which the length of this article precludes us from entering 

 upon at present. 

 August 8, 1828. J. Ivory. 



XXXIV. The Tables of Oltmanns for calculating Heights by 

 the Barometer > rendered applicable to English Barometers and 

 Measures. By H. T. De la Beche, Esq. F.R.S.* 



r T , HE French Board of Longitude have given these Tables 

 ■*■ in their Annuaire for the last two or three years, and 

 state that they appear to them " the most convenient of all 

 those hitherto published, for facilitating the calculation of 

 heights." After this eulogium it would be useless for me to 

 add any thing in favour of their merits, the chief of which 

 consists in their great simplicity. 



Being calculated for the metrical barometer, these tables 

 were useless to persons employing that graduated according 

 to English inches and their decimal parts. To render them 

 applicable to our barometers, I have prefixed a table (A), in 

 which the equivalent of every millimetre of the metrical baro- 

 meter is given in English inches and the hundredth parts of 

 inches, which is sufficiently close for all practical purposes. 



To reduce the metres used in these tables into English feet, 

 I have appended a table (F), where the number of English 

 feet corresponding to any number of metres up to 10,000 will 

 be immediately obtained. 



Abstraction being made of table A prefixed, and table F 

 appended, the march of operations is as follows : 



Let h be the height of the barometer at the lower station 

 expressed in millimetres ; h! that of the higher station ; T and 

 T' the temperature of the barometer at the different stations 

 according to the centigrade thermometer, t and t' that of the 

 air. 



We search in table B for the number which corresponds 

 to h ; let us call it a : we likewise search in the same table for 

 that which corresponds to /*'; let this be named b: let us call 



* Communicated by Mr. De la Beche. 



c, the 



