On hygrology, hygrometry, and their connexion with the phenomena observed in the atmosphere / by J. De Luc.

  • Luc, J. A. de (Jean André), 1727-1817.
Date:
1812
Catalogue details

Licence: Public Domain Mark

Credit: On hygrology, hygrometry, and their connexion with the phenomena observed in the atmosphere / by J. De Luc. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    given degrees of the hygro- meter still re- mained to be found. Mr. De Saus- sure's experi- ments objected to. The author resolved to re- peat them. 1st. objection. 2nd. objection. 3d. objection. quantities of moisture, and the degrees of my hygrometer; or what part each degree was of the whole: but I had not ob- tained a knowledge of the absolute quantity of evaporated water, which, in a given bulk of air, corresponded to these degrees ; a knowledge very essential in the investigation of the cause of rain. I saw that this was at least necessary for obtaining more certainty in meteorological conclusions. I relied in this respect on Mr. De Saussure’s experiments, as I had not yet had time to undertake them myself $ but I thought thendo repeat the same experiments, for the following reasons. 13. Mr. De Saussure had made these experiments with his hair •hygrometer, which was so dissimilar to mine in the rate of lengthening with the same increases of moisture, that his results could not be immediately applied to my instrument. But especially, he had made all these observations in the course of one day ; so that he could only obtain a few immediate points of comparison, whence he deduced a general law of the correspondence of the degrees of his hygrometer with the quantities of evaporated water in a given bulk of air. This was a first reason why some natural philosophers did not admit the results of his experiments. There were also some other rea- sons, which I shall hereafter mention : but these results were so important in meteorology, as he himself explained, that I resolved to repeat the same experiments in such a manner, as to remove all the objections, which I clearly saw could only affect the exactness of his experiments, but not their main results. I shall now mention all these objections, and the manner in which I proposed to remove them. 14. The first objection, as I have said above, was the short time employed in his experiments, to which he had been obliged by the nature of his vessel : I therefore wanted to use a vessel in which I could prolong these operations as long as I should find it necessary. A second objection had been made against the manner in which he first produced extreme dryness in his vessel, which was by new-calcined salt of tartar ; a substance which has chemical affinities with water, and might absorb air with it: I wanted therefore to use new-calcined lime, as I had used it for fixing the point of extreme dryness on my hygrometers. Lastly, there was an objection against the manner by which he had determined the quantities of evaporated water