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Hence there is reason to think that, contrary to the general opinion, 

 white garments are warmer than any other in cold weather ; and in- 

 deed if they are well calculated to reflect calorific rays in summer, 

 they ought to be equally well calculated to reflect those frigorific rays 

 by which we are annoyed in winter. Fur garments have been found 

 by experience to be much warmer in cold weather, when worn with 

 the hair outwards, than when it is turned inwards. 



This is alleged as a proof that we are kept warm by our clothing 

 not so much by confining the heat of our bodies, as by repelling those 

 frigorific rays which tend to cool us. The fur of several delicate 

 animals we know becomes white in winter in cold countries ; and 

 bears which inhabit the polar regions are likewise known to be white 

 in all seasons. Now if, in fact, as there is great reason to believe, 

 white is the colour most favourable to the reflection of calorific and 

 frigorific rays, it must be acknowledged that these animals have been 

 greatly favoured in having a clothing assigned them so well adapted 

 to their local circumstances. 



The excessive cold which is known to prevail, in all seasons, on 

 the tops of high mountains, and the frosts at night which frequently 

 take place on the surface of the plains below, seem to indicate that 

 frigorific rays arrive continually at the surface of the earth from every 

 part of the heavens ; and it is no doubt by the action of these rays 

 that our planet is continually cooled, and enabled to preserve the 

 same mean temperature for ages, notwithstanding the immense quan- 

 tities of heat that are generated at its surface by the continual action 

 of the solar rays. The action of these frigorific nocturnal rays will 

 likewise justify the inhabitants of hot climates, who, in order to be 

 more cool during their hours of rest, remove their beds in summer 

 to the tops of their houses. 



Experiments and Observations on the Motion of the Sap in Trees, In 

 a Letter from Thomas Andrew Knight, Esq. to the Right Hon. 

 Sir Joseph Banks, Bart. K.B. P.R.S. Read February 16, 1804. 

 [Phil. Trans. 1804, p. 183.] 



Some experiments are here described, the tendency of which is to 

 prove, what the author had advanced as a conjecture in a former 

 communication, that the vessels of the bark which pass from the 

 leaves to the roots, are in their organization better calculated to 

 carry the fluids they contain towards the roots than in the opposite 

 direction. 



In the first of these experiments several strong horizontal shoots 

 of vines were depressed about their middle ; and at that part, buried 

 in the mould, contained in pots about ten inches in diameter : after 

 some months of vegetation, when the shoots had nearly filled the 

 pots with roots, they were separated from the parent stock, having 

 at each side above the earth a certain length of the layer, with at 

 least one bud upon each. The end towards the stock was called the 

 inverted, and the other the proper end of the layer. If the author's 

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