1843.J Altitude of Purulia. 227 



By Mr. F. Baily's formula, each pair of the observations separately 

 calculated give 



8 a.m. Deduced altitude of Purulia, ... ... 663.62 feet 



10 a.m. ... Do 694.23 



4. p. m. ... Do 659.59 



Mean 672.48 



The Mean of the Observations gives .. .. 676.10 , 



And the same by Hutton's method, 674.77 



Final Mean 674.45 



Hence we may suppose that Purulia is about 670 feet above Ca 

 cutta. 



By reducing the Mean of the Barometers to the Mean Temperature 

 at Calcutta, we have 



Calcutta, 29496 



Purulia, 28.820 



Diff. 0.676 



I suppose this may be taken for the Barometrical equivalent. Indeed, 

 it appears that within moderate limits, and under similar temperature, 

 the Barometrical difference x 1000 = the difference of altitude be- 

 tween any two places in feet. It agrees very closely in this instance. 

 I have not seen the rule so simply stated, but it is nearly true, and 

 for the plains of India perhaps sufficiently so. The logarithmic rule 

 is, however, easy enough. 



