An Essay on Dew

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Excerpt from An Essay on Dew: And Several Appearances Connected With It I was led, in the autumn of 1784, by the event of a rude experiment, to think it probable, that the formation of dew is attended with the production of cold. In 1788, a paper on hoarfrost, by Mr. Patrick Wilson of Glasgow, was published in the first volume of the Transactions of the Royal Society of Edinburgh, by which it appeared, that this opinion had been entertained by that gentleman before it had occurred to myself. In the course of the same year, Mr. Six of Canterbury mentioned, in a paper communicated to the Royal Society, that, on clear and dewy nights, he always found the mercury lower in a thermometer laid upon the ground, in a meadow in his neighbourhood, than it was in a similar thermometer suspended in the air, six feet above the former , and that, upon one night, the difference amounted to 5° of Fahrenheit's scale. Mr. Six, however, did not suppose, agreeably to the opinion of Mr. Wilson and myself, that the cold was occasioned by the formation of dew , but imagined, that it proceeded partly from the low temperature of the air, through which the dew, already formed in the atmosphere, had descended, and partly from the evaporation of moisture from the ground, on which his thermometer had been placed. The conjecture of Mr Wilson, and the observations of Mr. Six, together with many facts, which I afterwards learned in the course of reading, strengthened my opinion , but I made no attempt, before the autumn of 1811, to ascertain by experiment if it were just, though it had, in the mean time, almost daily occurred to my thoughts. Happening, in that season, to be in the country on a clear and calm night, I laid a thermometer on grass wet with dew, and suspended a second, in the air, two feet above the other. An hour afterwards, the thermometer on the grass was found to be 8° lower, by Fahrenheit's division, than the one in the air. Similar results having been obtained from several similar experiments, made during the same autumn, I determined in the next spring to prosecute the subject with some degree of steadiness, and with this view went frequently to the house of one of my friends, who lives in Surrey. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.