Miscellaneous Intelligence. 07 



Condensation by Trees.— In heavy fogs, on elevated situations especially, 

 tr"es are perfect alembics : and no one that has not attended to such matters, 

 can imagine how much water one tree will distil in a night's time, by con- 

 densing- the vapour, which trickles down the twigs and boughs, so as to 

 make the ground below quite in a float. In Newton-lane, in October, 1775 

 on a misty day, a particular oak in leaf dropped so fast that the cart-way 

 stood in puddles, and the runs ran with water, though the ground in general 

 was dusty. 



In some of our smaller islands in the West Indies, if I mistake not, there 

 are no springs or rivers : but the people are supplied with that necessary 

 element, water, merely by the dripping of some large tall trees, which, stand- 

 ing in the bosom of a mountain, keep their heads constantly enveloped with 

 fogs and clouds, from which they dispense their kindly never-ceasing mois- 

 ture ; and so render those districts habitable by condensation alone. 



Trees in leaf have such a vast proportion more of surface than those that 

 are naked, that, in theory, their condensations should greatly exceed those 

 that are stripped of their leaves: but, as the former imbibe also a great 

 quantity of moisture, it is. difficult to say which drip most: but this I know, 

 that deciduous trees that are entwined with much ivy seem to distil the 

 greatest quantity. Ivy leaves are smooth, and thick, and cold, and therefore 

 condense very fast ; arid besides ever-greens imbibe very little. These facts 

 may furnish the intelligent with hints concerning what sorts of trees tliey 

 should plant round small ponds that they would wish to be perennial; and 

 shew them how advantageous some trees are in preference to others. 



Trees perspire profusely, condense largely, and check evaporation so 

 much, that woods are always moist : no wonder, therefore, that they contri- 

 bute much to pools and streams. 



That trees are great promoters of lakes and rivers, appears from a well- 

 known fact in North America; for, since the wood.-, and forests have been 

 grubbed and cleared, all bodies of water are much diminished; so that 

 some streams, that were very considerable a century ago, will not now drive 

 a common mill.* Besides, most woodlands, forests, and chases, with us 

 abound with pools and morasses; no doubt for the reason given above. 



To a thinking mind i'cw phenomena are more strange than the state of 

 little ponds on the summits of chalk-hills, many of which are never dry '.n 

 the most trying droughts of summer. On chalk-hills I say, because in many 

 rocky and gravelly soils, springs usually break out pretty high on the sides 

 of elevated grounds and mountains; but no person acquainted with chalky 

 districts will allow that they ever saw springs in such a soil hut in valleys 

 and bottoms, since the waters of so pervious a stratum as chalk all lie on 

 one dead level, as well-diggers have assured me again and again. 



Now, we have many such little round ponds in this district; and one in 

 particular on our sheep-down, three hundred feet above my house; which, 

 though never above three feet deep in the middle, and not more than thirty 

 feet in diameter, and containing perhaps not more than two or three hundred 

 hogsheads of water, yet never is known to fail, though it affords drink for 

 three hundred or four hundred sheep, and for at least twenty head of large 

 cattle besides. This pond, it is true, is overhung with two moderate 

 beeches, that, doubtless, at times, afford it much supply; but then we 

 have others as small, that, without the aid of tie::-;, and in spite of evapora- 

 tion from sun and wind, and perpetual consumption by cattle, yet constantly 

 maintain a moderate share of water, without overflowing in the wettest 

 seasons, as they would do if supplied by springs. By my journal of May, 

 1775, it appears that "the small and oven considerable ponds on the vales 

 are now dried up, while the small ponds on the very tops of hills are hut. 

 little affected." Can this difference be accounted for from evaporation alow . 

 which certainly is more prevalent in bottoms? or rather have not those 

 elevated pools some unnoticed recruits, which in the night lime counter- 

 balance the waste of the day; without which the cattle alone must so"n 

 exhaust them ? And here it will he necessar) to inter more minutely into 

 the cause. Dr. Hales, in his Vegetable Statics, advances, from experi'mcii. 

 that "t!u- moister the earth is, (he more dew falls on it in a night : and more 

 than a double e,-;antity of dew falls on a surface of water (ban Ibere does on 



• Vide Ka'.m's Travels to North America. 



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