338 ON PHYSICAL DATA 



How far each of these individual causes conspire 

 to produce the variation of the barometer is a 

 question of extreme difficulty to answer. The 

 following are the data which seems to me to be 

 desirable to obtain in order to give a full and 

 explicit exposition to the above inquiry. 



1st. As the extreme limits of the barometer 

 are obtained, often with great rapidity, the time 

 of obtaining its maximum and minimum points, 

 with the time those points remain stationary, 

 should be constantly observed at different points 

 on the earth's surface. 



2nd. That when evaporation takes place, either 

 from the surface of land or from water, the total 

 quantity of evaporation, with its density at any 

 temperature, ought to be carefully ascertained. 



These are amongst the data which ought to be 

 taken in order to enable the mathematician to 

 give a solution to the following problem : 



Given the initial circumstances of the atmos- 

 phere at any epoch, together with the laws which 

 regulate the transmission of fluid pressure from 



