the Barometric Formula;, ^c. 649 



state of the atmosphere, confessedly erroneous as to temperatures below the 

 freezing-point, has been shown to be erroneous for temperatures also above the 

 freezing-point. The constant recommended by Laplace has been proved to be 

 too small, and has been replaced by a constant obtained by the consideration 

 of the ratio of the specific gravity of dry air to that of quicksilver, and the con- 

 stant thus obtained is necessarily more correct than a constant obtained by 

 means of observations, however nvunerous, barometric, hygrometric, and ther- 

 mometric. This better way of obtaining the constant has been rendered 

 available by the peculiarities of the new formula, and it is in this point of view 

 that the new formula is so peculiarly valuable. 



The indispensable necessity of tables of horary correction, in order to 

 obviate the mean temperature errors, is placed beyond the possibility of con- 

 troversy, and the importance of the new formula as a valuable help to work 

 out hereafter such tables has been made apparent. 



But we are warned by the facts of this paper, that with even the assistance 

 of a sound table of local horary corrections, we are not to expect exemption 

 from serious error on all occasions ; it is, however, satisfactory to know that 

 where error be not altogether excluded, it is diminished at least one-half by the 

 working of the new system. 



Moreover, the heights calculated by the new formula agree in a very satis- 

 factory manner with the working of a formula of the same kind given by Bessel, 

 in use on the Continent. Its superiority to that of Bessel appears by simple 

 inspection. But forasmuch as the trouble of making hygrometric observations 

 is not small, and as the advantage of such trouble on ordinary occasions is not 

 great, in order to dispense with such trouble I have given a peculiar formula, 

 peculiarly simple, which on ordinary occasions renders hygrometric observations 

 unnecessary, and yet makes provision sufficiently correct for the hygrometric 

 state of the atmosphei'e. 



4q2 



