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Reviews and JS^otices of Books. 



cise a powerful infiuence over the climate of a country; and it is 

 to the influence of two such currents that the British Isles owe 

 their singularly mild, equable, and healthy climate. The Florida 

 Gulf stream impinges on our western shores, bringing with it the 

 warmer temperature of southern latitudes ; and since the prevail- 

 ing direction of the wind is south-west, a higher temperature is 

 imparted to the British Isles in common with the whole of Wes- 

 tern Europe. The south-western parts of Ireland and Great 

 Britain receive the greatest benefit, and these places accordingly 

 are the favourite residences of invalids during winter, and they 

 may also be noticed as famous for the early growth of vegetables 

 for the London market. The western coasts of South America 

 may be referred to as illustrating the effects of a cold oceanic 

 current flowing from the Polar Seas, and thus reducing the tem- 

 perature of those parts by w^hich it passes. Thus the mean 

 temperature of Callao in 12° S. Lat. is only 68°'9, while that of 

 Bio Janeiro in 23° S. Lat. is 73°-8. 



The following important practical remark is made in discussing 

 the temperature of the soil: — 



" It is known that every plant requires a certain amount of 

 heat, varying in the case of each species, for the renewal of its 

 growth at the commencement of the season. 



" i^ow when this degree of heat has spurred into activity those 

 parts that are above ground, and caused them to elaborate the 

 sap, it is necessary that the subterranean portions should at the 

 same time be excited by the heat of the ground to absorb the 

 materials which are to supply the plant with nourishment. Un- 

 less the latter function is provided for, the aerial portions of the 

 plant will languish from want of food to assimilate. Indeed, it 

 is even advisable that the roots should take the start of the leaves, 

 in order to have in readiness a store of food for the latter to draw 

 upon." 



It is only in well-drained well-pulverised soils that plants 

 enjoy the fullest benefit of this consideration ; for, as has been 

 shown in the Scottish Meteorological Society's Beport for the 

 quarter ending December 1862. the effect of draining is, — by 

 drawing off the water, and thus filling the interstices of the soil 

 with air which is about the w^orst conductor of heat, — to prevent 

 the penetration of frosts into such soils to any great depth. 



The next most important element of climate is the moisture of 

 the air. 



" We must, however, carefully distinguish between the humi- 

 dity present in the atmosphere in the form of vesicular vapour, 

 and that existing in it in an invisible or aeriform condition. 



" All liquids have a tendency to pass into vapour, until checked 

 by the pressure of their oiva atmosphere ; and this tendency, 



