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[ 2 ] meter, the scales of Fahrenheit, Delisle Reaumur, &c.
3d. Constancy in the variations produced by the same differences of humidity. 2. I perceived, moreover, that it were to be wished, that the hygrometer should give a true indication of the relation between the real quantit e sof the humi- dity, or at least between their differences: but this last point I rather considered as a desirable degree of per- fection, than as an indispcnsablc requisite; the effen- tial point being, that observers might understand each other, when mentioning degrees of humidity ; and this seemeed to be sufficiently provided for by the abovementioned conditions. 3· Having thus planned to myself the work I had to go through, I first attended entirely to the first point, and laid aside all the others. This I again subdivided. I had soon perceived that I must begin by thinking much less of the hygrometer than of the different phænomena of humidity. For this pur pose it was necessary to find out a fixed state, either of bodies in general, or of same body in particular ; and this fixed state might either be extreme humi dity, or dryness, or any intermediate point 4· Knowing that the extremes in nature are com monly very difficult. and sometimes impossible to hit, I conceived at first greater hopes of intermediate degrees. But in vain did my imagination fatigue it self in a road, which I was forced to abandon. 5· I then came to the extremes, and that of abso lute dryness was the first I was induced to try. But having found no other way to procure it but by fire, and fire not producing it in all bodies which appearet do.