An Essay on Dew: And Several Appearances Connected with it

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Taylor and Hessey, 1815 - 150 pages
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Page 4 - One general fact relative to situation is, that whatever diminishes the view of the sky, as seen from the exposed body, occasions the quantity of dew, which is formed upon it, to be less than would have occurred, if the exposure to the sky had been complete.
Page 54 - These examples are sufficient to shew the value of the fact, that bodies become colder than the neighbouring air, before they are dewed, in explaining many atmospherical appearances. To this point, the investigation of the cause of dew might have been carried at any time, since the invention of thermometers ; but its complete theory could not possibly, in my opinion, have been attained, before the discoveries on heat were made, which are contained in the works of Mr. Leslie and Count Rumford.
Page 112 - I had often, in the pride of half knowledge, smiled at the means frequently employed by gardeners to protect tender plants from cold, as it appeared to me impossible that a thin mat, or any such flimsy substance could prevent them from attaining the temperature of the atmosphere, by which alone I thought them liable to be injured. But when I had learned that bodies on the surface of the earth become, during a still and serene night, colder than the atmosphere, by radiating their heat to the heavens,...
Page 112 - ... the country, though in a less degree than during the day, as the clouds will remit towards the earth no inconsiderable quantity of heat. But on a clear night, in an open part of the country, nothing almost can be returned to us from above, in place of the heat which we radiate upwards.
Page 118 - For their outermost twigs, now that they are destitute of leaves, are much smaller than the thermometers suspended by me in the air, which in this situation very seldom became more than 2° colder than the atmosphere. The larger branches too, which, if fully exposed to the sky, would become colder than the extreme parts, are, in a great degree, sheltered by them ; and, in the last place, the trunks are sheltered both by the smaller and the larger parts, not to mention that the trunks must derive...
Page 66 - A greater quantity of dew has also been observed to form betweeen midnight and sunrise than between sunset and midnight." " The appearance of dew is not confined to any one part of the night, but occurs during its whole course, from means the most simple and efficacious. For after one part of the air has deposited its moisture on the colder surface of the earth, it is removed in consequence of that agitation in the atmosphere which exists during its stillest states, and gives place to another having...
Page 116 - Possibly, experience has long ago taught gardeners the superior advantage of defending tender vegetables, from the cold of clear and calm nights, by means of substances not directly touching them ; though I do not recollect ever having seen any contrivance for keeping mats, or such like bodies, at a distance from the plants, which they were meant to protect. Walls, I believe, as far as warmth is concerned, are regarded as useful, during a cold night, to the plants which touch them, or are near to...
Page 113 - ... that of neighbouring grass which was uncovered, if this was colder than the air. When the difference in temperature, between the air several feet above the ground and the unsheltered grass, did not exceed 5°, the sheltered grass was about as warm as the air. If that difference, however, fixxieeded 5°, the air was found to be somewhat warmer than the sheltered grass.
Page 7 - ... while 10 grains of wool, laid upon the raised board, increased 20 grains in weight, an equal quantity, suspended in the open air, 5£ feet above the ground, increased only 11 grains, notwithstanding that it presented a greater surface to the air than the other parcel. On another night, 10 grains of wool gained on the raised board 19 grains, but the same quantity suspended in the air, on a level with the board, only 13; and on a third, 10 grains of wool acquired, on the same board, 2£...

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