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in my hygrometers, I think it reasonable to hope that this instrument will receive a sensible degree of perfection on a second trial ; and that in time it will be brought to a sufficient degree of accuracy. It is true there are some difficulties in the way of this: but have we not sufficient motives for endeavoring to overcome them? The air we breathe, and that which surrounds us ; the places we inhabit, and those which serve either to enclose or to preserve so many different bodies intended for our several occasions are all of them more or less filled with that substance, differently modified, to which I have given the name of humor. It also produces very sensible effects in them ; some of which very properly excite our curiosity, others may be turned to our advantage, and many of them essentially affect our health. It is therefore of great consequence to natural philosophy in general, and to economy, and medicine, in particular, that we should obtain a measure by which we may, with some degree of certainty, estimate the local and actual qualities of this substance and by this means foresee its effects; which for the generality we only become acquainted with after they are produced These sciences are not perhaps less concerned that we should discover the nature itself of this agent, and the different manners in which it ope- rates: the knowledge of which may enable us to avail ourselves of reason in the investigation of certain effects, which, without such helps, might escape our observation As these are the several uses of an exact hygrometer, we may readily perceive how many new tracts such an instrument may open to us, in our investigations of nature, which however F 2
