_For the_ mean _Pressure of the Barometer, at low Water, from 132 Observations in Italy and England, is 30.04 Inches: the Temperature of the Barometer being at 55°, i.e. Temperate, and that of the Air at 62°._ [122] _Foundation of the Table for Tenths._ The Height, in _Feet_, corresponding to the Expansion on the Tenth of an inch of Quicksilver with the Temperature of 31°.24 (as in the 3d Column of the 2d Table) are reduced by this Table into a ten Times less Number of Feet; and the Tenth of an Inch (of Quicksilver) is also again divided into _ten_ more Parts: in order to shew, in a ten Times less Number of _such_ Feet, the Expansion corresponding to any of those Parts into which the _Tenth_ of an Inch (of Quicksilver) has been divided. _Construction and Use of the Table for Tenths._ 1. The Figures in the left vertical Column shew the Height in _Feet_, (from 81 to 130) corresponding to a single Tenth of an Inch of Quicksilver, viz. to the higher of two adjoining Tenths, as in the 3d Column of the 2d Table. 2. The Figures, along the upper horizontal Line, shew the Number of Parts into which the Tenth of an Inch has been divided. 3. The Figures, at the Point of Meeting, express, in a ten Times less Number, of _the Feet_ in the left vertical Column, the Expansion corresponding to any of those Parts, into which the Tenth of an Inch (of Quicksilver) has been divided. Thus: 90 is a _Number of Feet_ called 9 Tenths of 100: but the _Tenths_ are _Feet_, and not Tenths of a Foot. [123] The Standard Temperature was 31°.24, which not being exactly 1 Quarter, another Decimal is added, (for Ease in Computation,) by which 31.24 becomes 31.25, i.e. by dividing one Degree of Heat into 100 Parts, and taking 25 of those Parts, or dividing the 100 by 25, the Answer is 4, i.e. ¼ of the whole 100: or (31)¼. [124] _The Foundation of the fourth Table._ (Ph. Tr. for 1777, Part 2d, Pages 564, and 566,)—From the _Mean_ of a Series of Experiments with a Manòmeter, or Instrument to measure the _Rarity_ and Density of the Atmosphere, depending on the Action of _Heat_ and Cold, it was found, that when the _Portion of a Tube_ containing Air (at the Temperature of freezing by Farenheit, and Pressure of 30½ Inches[125] by a common Barometer) was divided into 1000 Parts; the Volume of _Air_ within it, encreased _nearly_ in a certain Proportion, as each Degree of Temperature encreased; viz. at a Mean, 2.43, or simply (by rejecting the 2d Decimal as too minute) 2.4: that is, a 1000 Parts of Air became by Expansion with one Degree of the Thermometer, equal to 1002.43: i.e. the Portion of Air occupying 1000 Parts, did, with the Addition of one Degree of Heat, occupy 1002.43 Parts: that is (by rejecting the 2d Decimal 3 as too minute) occupied two Parts and 4 Tenths more than the thousand. _Construction of the fourth Table._