. The book of the garden. Gardening. CAUSE OF CIRCULATION OF HOT WATER. 267 bend, so as to form a siphon, may rise higher than the feeding cistern c and air- pipe a; but this construction is danger- ous, inasmuch as air may accumulate in the bend and stop the circulation. It is better, therefore, to make the cistern c and air-pipe a higher than any required elevation in the water-pipes, as m, and furnish the latter with a small pipe to carry off the air. Every such ascent and descent evidently creates a force of some amount in favour of the movement, not, perhaps, more than enough to balance t
. The book of the garden. Gardening. CAUSE OF CIRCULATION OF HOT WATER. 267 bend, so as to form a siphon, may rise higher than the feeding cistern c and air- pipe a; but this construction is danger- ous, inasmuch as air may accumulate in the bend and stop the circulation. It is better, therefore, to make the cistern c and air-pipe a higher than any required elevation in the water-pipes, as m, and furnish the latter with a small pipe to carry off the air. Every such ascent and descent evidently creates a force of some amount in favour of the movement, not, perhaps, more than enough to balance the increased friction produced by the bends, because the temperature of the ascending and descending columns cannot differ much. When it is, however, necessary to make a descent, as n, the difference of temperature in the two columns is ad- verse to the movement; and as this acts in addition to the retardation produced by the changes of direction, such descents should be cautiously made, and only when there is an obvious preponderance of power to carry the water through them. " In such a system as that described in the figure, where the vertical pipes may be called from 5 to 10 feet, and where there are no descending bends like n, it is surprising through what an immense length of nearly horizoDtal pipes the cir- culation may be carried. I believe," he says, "that the limits are not known; and, as the friction of many hundred feet of pipe must be considerable, though it is less than is generally supposed, the effect seems to require some more powerful cause than the different weights of the two columns. Various speculations have been made with the view of accounting for this, but I am not," he says, " aware of any that is quite satisfactory, and the following may be as little conclusive. It appears to me, however, that the con- tinual cooling of the water furnishes a material facility towards its movement. Referring to the last fig., (348,) if % be supp
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectgardening, bookyear18
