Secondly, Those, that will be so curious, may, instead of the Ordinary Counterpoise (of Brass) employ one of Gold, or at least of Lead, whereof the latter being of equal weight with Brass, is much less in Bulk, and the former amounts not to half its bigness.
Thirdly, These parts of the Ballance, that may be made of Copper or Brass, without any prejudice to the exactness, will, by being made of one of those Mettals, be less subject, than Steel, (which yet, if well hardned and polish'd, may last good a great while) to rust with long standing.
Fourthly, Instead of the scales, the Buble may be hung at one end of the Beam, and only a Counterpoise to it at the other, that the Beam may not be burthen'd with unnecessary weight.
Fifthly, The whole instrument, if placed in a small Frame, like a square Lanthorn with Glass-windows, and a hole at the top for the Commerce of the internal and external Air, will be more free from dust, and irregular agitations; to the latter of which, it will otherwise be sometimes incident.
Sixthly, This instrument being accommodated with a light Wheele and an Index (such as have been applyed by the excellent Dr. Chr. Wren to open Weather glasses, and by the ingenious Mr. Hook to Baroscopes) may be made to shew much more minute variations, than otherwise.
Seventhly, And the length of the Beam, and exquisitness of the Ballance, may easily, without any of the foregoing helps (and much more with them) make the instrument far exacter, than any of those, I was reduced to employ. And to these Accommodations divers others may be suggested by a farther consideration of the nature of the thing, and a longer practice.
Though in some respects this Statical Baroscope be inferior to the Mercurial; yet in others it has its own advantages and conveniencies above it.
And 1: It confirms ad oculum our former Doctrine, that the falling and rising of the Mercury depends upon the varying weight of the Atmosphere; since in this Baroscope it cannot
be pretended, that a Fuga vacui, or a Funiculus, is the cause of the changes, we observe. 2. It shews, that not only the Air has weight, but a more considerable one, than some Learned men, who will allow me to have prov'd, it has some weight, will admit; since even the variation of weight in so small a quantity of Air, as is but equal in bulk to an Orange, is manifestly discoverable upon such Balances, as are none of the nicest. 3. This Statical Baroscope will oftentimes be more parable, than the other: For many will finde it more easie, to procure a good pair of Gold-scales, and a Buble or two, than a long Cane seal'd, a quantity of Quick-silver, and all the other requisits of the Mercurial Baroscope; especially if we comprise the trouble and skill, that is requisite to free the deserted part of the Tube from Air. 4. And whereas the difficulty of removing the Mercurial Instrument has kept men from so much as attempting to do it, even to neighbouring places; the Essential parts of the Scale-Baroscope (for the Frame is none of them) may very easily in a little room be carried, whither one will, without the hazard of being spoil'd or injur'd. 5. There is not in Statical Baroscopes, as in the other, a danger of uncertainty, as to the goodness of the Instruments, by reason, that in these the Air is, in some more, and in some less perfectly excluded; whereas in those, that consideration has no place. (And by the way, I have sometimes, upon this account, been able to discover by our new Baroscope, that an esteem'd Mercurial one, to which I compared it, was not well freed from Air.) 6. It being, as I formerly intimated, very possible to discover Hydrostatically, both the bigness of the Buble, and the Contents of the cavity, and the weight and dimensions of the Glassie substance (which together with the included Air make up the Buble,) much may be discover'd by this Instrument, as to the Weight of the Air, absolute or respective. For, when the Quick-silver in the Mercurial Baroscope is either very high, or very low, or at a middle station between its greatest and least height, bringing the Scale-Barometer to an exact Æquilibrium (1 with very minute divisions of a Graine,) you may, by watchfully observing, when the Mercury is risen or faln just an inch, or a fourth, of half an inch &c. and putting in the like minute divisions of a Grain to the lighter Scale, till you have again brought the Ballance to an
exquisit Æquilibrium; you may, I say, determine, What known weight in the Statical Baroscope answers such determinate Altitudes of the ascending and descending Quick-silver in the Mercurial. And if the Ballance be accommodated with a divided Arch, or a Wheel and Index, these Observations will assist you for the future to determine readily, by seeing the inclination of the Cock or the degree mark'd by the Index, what pollency the Buble hath, by the change of the Atmospheres weight, acquired or lost. Some Observations of this nature I watchfully made, sometimes putting in a 64th. sometimes a 32th. sometimes a 16th. and sometimes heavier parts of a Grain, to the lighter Scale. But one, that knew not, for what uses those little papers were, coming to a window, where my Baroscopes stood, so unluckily shook them out of the Scales, and confounded them, that he robb'd me of the opportunity of making the nice Observations I intended, though I had the satisfaction of seeing, that they were to be made. 7. By this Statical Instrument we may be assisted to compare the Mercurial Baroscopes of several places (though never so distant) and to make some Estimates of the Gravities of the Air therein. As if, for instance, I have found by Observation, that the Buble, I employ, (and one may have divers Bubles of several sizes, that the one may repaire any mischance, that may happen to another) weigh'd just a Drachme, when the Mercurial Cylinder was at the height of 29½ inches (which in some places I have found a moderate altitude;) and that the Addition of the 16th part of a gr. is requisite to keep the Buble in an Æquilibrium, when the Mercury is risen an 8th, or any determinate part of an inch above the former station: When I come to another place, where there is a Mercurial Barometer, as well freed from Air as mine (for that must be supposed) if taking out my Scale instrument, it appeare to weigh precisely a Drachme, and the Mercury in the Baroscope there stand at just 29½ inches, we may conclude the Gravity of the Atmosphere not to be sensibly unequal in both those two places, though very distant. And though there be no Baroscope there, yet if there be an additional weight, as for instance, the 16th part of a Grain requisite to be added to the Buble, to bring the scales to an Æquilibrium, it will appear that the Air at this second place is, at that time