318 



Mr. Hinds on Climate in connexion 



a further compensation ; when the temperature is sufficiently 

 depressed the insensible moisture is precipitated, and the 

 caloric necessary to its existence as an aeriform body is given 

 out and becomes sensible. 



The relative proportion of moisture in the atmosphere varies 

 vrith circumstances ; temperature has a powerful influence over 

 the quantity suspended, and a change in the amount occurs 

 as the temperature alters through the seasons. Alterations 

 of temperature in small intervals of time have but a trifling 

 effect, and it is rather the mean heat of a reasonable portion 

 that it follows. Between the conditions of the vapour of the 

 atmosphere and the circumstances of evaporation there are 

 such points of resemblance, that an estimate of one puts us in 

 possession of the chief features of the other. The mean tem- 

 peratures have been seen to advance as the latitude is dimi- 

 nished, or as the equator is approached, and the activity of 

 evaporation and the quantity of suspended vapour proportion- 

 ately increase from the poles to the equator. The higher the 

 mean temperature, other things being the same, the greater is 

 the force of evaporation, and necessarily the quantity of 

 moisture suspended in the air. 



Not many data have hitherto been obtained as to the 

 amount of evaporation in different latitudes, or under a variety 

 of mean temperatures. To supply this deficiency a table has 

 been calculated for the rate of evaporation for every 5° from 

 the equator to the pole ; it has been constructed on the ad- 

 mission that the deposition of moisture takes place in England 

 at 6° below the mean temperature. It is not improbable that 

 the mean point of deposition below the mean temperature 

 varies very little in different latitudes, and that a depression 

 of 6° below the mean will be nearly as correct for the tropics 

 as for our own climate. 



This table is theoretical, and constructed on the foundation 



