AS COMPARED WITH AN UN WOODED. 15 



according to circumstances in producing rainfall, there must always 

 be others, which, although entirely local, and probably therefore 

 more difficult to define or specify, are nevertheless of considerable 

 potency in their agency, and these must be known before we can 

 determine the climate of any locality with regard to humidity. In 

 fact, curious and conflicting discrepancies may ffequently be observed 

 between the quantity of rain which falls in two situations proximately 

 situated to each other, and at the same altitude, at the same distance 

 from the sea, and exposed to the same wind, which will then force 

 upon us the undeniable conclusion that the variation is duo to 

 local shelter, or from the one situation being exposed (while the 

 other is not) to moist winds, being situated ou a height, or in a 

 valley. We may here mention a fact which has been frequently 

 observed. When the clouds, wind-driven, and careering along at 

 no great elevation above the earth's surface, approach or encounter a 

 mountain, or sometimes even a small hill only, they are seen per- 

 haps to rise, and attaining thus to a colder stratum of air, they 

 become condensed into rain ; and may we not, therefore, believe 

 that forests or plantations of timber, when the clouds are very low, 

 produce the same results, varying probably with the seasons ? Of 

 course, any such influence will be intensified, and rendered the more 

 sensitive, in proportion to the area of the plantation or forest, and 

 as the masses of woodland are more or less considerable. Upon this 

 point, however, until the contemplated hygrometric observations 

 from a variety of stations under suitable conditions have been 

 obtained and tabulated, it is impossible to speak with anything like 

 certainty ; and it is just one of those many interesting points which, 

 apart from all theory or preconceived notions on the subject, it is 

 desirable to settle conclusively if practicable, and that can only be 

 done in any complicated problem or dark unsolved mystery, by 

 applying to it the lantern of experiment and careful observa- 

 tion. This necessitates the establishment in different parts of the 

 country of observatories, in each of which daily records must be 

 made of the temperature of the air and of the sun, as well as of the 

 quantity of water which falls under woods, on the margins of the 

 same plantations, and at distances more or less remote from these 

 woods. For a society like the Scottish Arboricultural Society, it 

 may be perhaps better, at first, at all events, to confine the registers 

 of its observers only to the rain-gauges in these situations, leaving 

 those concerning the thermometers, as optional at present, upon 

 those willing to undertake their registration. 



