So far as the observations have at present been made, they 

 point out some defects in the data relative to great distances, 

 which probably may be supplied by a well regulated course of ob- 

 servations. 



Good observers have often found an irregularity in the results 

 when the weather has been whidy ; and if the cause of the wind 

 be duly considered, there will appear some probability of the 

 necessity for taking into the account the direction and velocity 

 of the wind in addition to that of the heat of the mercury and 

 of the surrounding air. Because, if there were not some local 

 inequality in the pressure of the atmosphere, there would be no 

 wind, to restore tlie equilibrium, any more than there would be a 

 current in a lake without the addition or subtraction of a quan- 

 tity to or from the primary bulk. 



This inequality of pressure may be supposed to cause a wave 

 on the superior parts of the atmosphere, requiring a suitable al- 

 lowance to one of the instruments before a proper deduction can 

 be made of the relative altitudes. 



To ascertain the law of this allowance, it will require a good 

 course of well arranged observations at places of known distances 

 and difference of elevations under a variety of states of the wind, 

 both as to direction and force. But a single course one day in 

 a month cannot be expected to produce a satisfactory result in a 

 reasonable time : it is to be hoped that some other course will be 

 adopted. Yours truly. 



To Mr. Tilloch. B. Blvan. 



METEORO- 



