334 ON PHYSICAL DATA 



The Rain Gauge is an instrument adapted 

 lo ascertain the amount of rain deposited in the 

 locality where it is placed, and for many pur- 

 poses connected with the trade and commerce of 

 this country, the average amount of rain, which 

 falls at different places, is very desirable and 

 useful to know ; in connection with an accurate 

 acquaintance with the geological deposition and 

 chemical properties of the strata on which it falls. 

 But for philosophical purposes, it appears to me 

 to be desirable to ascertain, not only the amount 

 of rain which falls, but the outline of the space 

 in which rain is descending, and the direction 

 and force of the wind. 



With respect to the variations of the Barome- 

 ter, there appears to be a great variety of 

 opinions amongst the cultivators of meteorologi- 

 cal science ; these I shall pass over, and proceed 

 to state the elements which, I conceive, ought to 

 be carefully observed. Hitherto, observations 

 have been conducted principally with a view to 

 discover the relation between the amount of 

 water disengaged from the atmosphere, and the 

 weight of a column of atmospheric air, no relation 

 however between these two elements has yet been 

 determined. The time during which the mercury 



