It will be requisite also, that the Observers give notice of the _Scituation of the place_, where their _Barometers_ stand, not only, because it will assist men to Judge, whether the Instruments were duely perfected, but principally, because, that though the _Baroscope_ be good (nay, because it is so) the Observations will much disagree, even when the _Atmosphere_ is in the same state, as to Weight, if one of the Instruments stand in a considerably higher part of the Countrey, than the other. To confirm _both_ the foregoing admonitions, I must now inform you, that, having in these parts two Lodgings, the one at _Oxford_, which you know stands in a bottom by the _Thames_ side, and the other at a place four miles thence, seated upon a moderate _Hill_, I found, by comparing two _Baroscopes_, that I made, the one at _Oxford_, the other at _Stanton St. Johns_, that, though the former be very good, and have been noted for such, during some years, and the latter was very carefully fill'd; yet by reason, that in the _Higher_ place, the incumbent part of the _Atmosphere_ must be lighter, than in the _Lower_, there is almost {183} always between 2 and 3 Eights of an Inch difference betwixt them: And having sometimes order'd my servants to take notice of the Disparity, and divers times carefully observ'd it my self, when I pass'd to and fro between _Oxford_ and _Stanton_, I generally found, that the _Oxford Barometer_ and the _other_, did, as it were by common consent, rise and fall together so, as that in the former the _Mercury_ was usually 3/8 higher, than in the latter. Which Observations may teach us, that the Subterraneous steams, which ascend into the Air, or the other Causes of the varying Weight of the _Atmosphere_, do, many times, and at least in some places, uniformly enough affect the Air to a greater height, than, till I had made this tryall, I durst conclude. But, as most of the _Barometricall_ observations are subject to exception, so I found the formerly mentioned to be. For (to omit lesser variations) riding one evening from _Oxford_ to _Stanton_, and having, before I took horse, look't on the _Baroscope_ in the former of these 2. places, I was somewhat surprised, to find at my comming to the latter, that in places no farther distant, and notwithstanding the shortness of the time (which was but an hour and a half, if so much) the _Barometer_ at _Stanton_ was short of its usual distance from the _other_, near a quarter of an _Inch_, though, the weather being fair and calm, there appear'd nothing of manifest change in the Air, to which I could adscribe so great a Variation; and though also, since that time, the _Mercury_ in the two Instruments hath, for the most part, proceeded to rise and fall as before.