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[ 19 ] 12 gr. or 1428 grains. All the pieces of my hygrometer being put together, it weighed 373 grains,

and when filled with the properquantity of mercury

833. It consequently contained 460 grains of mercury.

46. By the rule above given (23), the extent of the hygrometer's degrees, ought to be to that of the degrees in the prepatory thermometer, in proportion of the respective weights of mercury in the hygrometer and thermometer ; and consequently as the weight of the mercury in the thermometer is to the weight of the mercury in the hygrometer, so is any given interval in the thermometrical scale, to the corresponding interval in the scale of the hygrometer. Consequently in our example as 1428 460 1937 624 (nearly) ; and the corresponding intervals on the scales of the thermometer and the hygromter, ought to follow the proportion of 1937 to 624.

47. I call the distance between the two fixed points of heat in the thermometer the fundamental interval ; and I shall call the fundamental line in the hygrometer that of which the length corresponds to this interval. Thus the fundamental interval in the prepatory thermometer, being 1937 parts of a certain scale, the fundamental line of my hygrometer consisted of 624 parts of the same scale. This may so easily be applied, tha it will be unneccessary to dwell any longer upon this subject.

48. Having thus got a fundamental line in the hygrometer, I had it in my power to divide it into as many parts as I thought proper : my choice was D 2 naturally