355. 3d Step. Subtract the _colder attached_ Thermometer, from the other attached Thermometer, thus: 46 colder from 50 warmer, and there remains 4° warmer, viz. the Number of Degrees of Temperature to which the _colder_ Barometer must be _expanded_, before it becomes equal in Temperature to the _warmer_ Barometer: each Barometer being always supposed _equal_ in Temperature with its _attached_ Thermometer. 356. 4th Step. Give the _colder_ Barometer the same _Temperature_ with the warmer: or, which amounts to the same, give the _colder_ Barometer that _Expansion_ which is communicated by the Addition of 4 Degrees of Temperature. Both Barometers will then have the same _Temperature_, or _Expansion_, viz. an Expansion equal to the warmer Barometer. This is to be done by referring to the first Table, for the Application of which there are separate Instructions: see the Explanation of the first Table.[118] CHAPTER LXXI. USE AND PRACTICE OF THE FIRST TABLE, IN THE FIRST EXAMPLE. _The_ +use+. Section 357. To find the Expansion of Quicksilver, and of the barometric Tube in which it is contained: or, in other Words, to find the Point to which the Quicksilver will rise in the Tube, (in Parts of an Inch) with a given additional Temperature, on Farenheit’s Scale. The Question in the first Example is, (Ph. Tr. for 1777, Page 578;) To find the Expansion that arises, _with_ the Addition of 4 Degrees of Heat, _on_ the _colder_ Barometer resting at Inches 25 .19 Tenths, in order to give it an Expansion equal to that of another Barometer, 4 Degrees warmer than the former: the Temperature of _each_ Barometer, being indicated by its respective _attached_ Thermometer. N. B. During the Application of the first Table, the Investigation moves forward two Steps only, viz. the 4th and 5th. _The 4th Step, applied in the first Example._ 358. The _Order_ to be observed in finding the Expansion of the Quicksilver, with 4 Degrees on Inches 25 .19 Tenths of the Barometer. 1st. Find the Expansion, With 4° on 25 Inches only. Then in order to obtain with 4° on .19, begin 2d. With 4° on 1 Inch above 25 Inches, i.e. on the 26th Inch. 3d. With 4° on .1, i.e. one Tenth of an Inch above 25 Inches: and lastly, 4th. With 4° on .19, Tenths above 25 Inches. _The_ +practice+. 359. 1st. In the _first_ Table, _with_ 4 Degrees on the left Hand vertical Column, and with 25 Inches, along the upper Range; at the Point of Meeting, is the Answer .0101[119] viz. the Expansion, or Rise of the Quicksilver standing at 25 Inches, and receiving an additional Heat of 4°: the Answer .0101 being the Expression for the ten thousand one hundredth Part of an Inch, (viz. in Height, by Expansion.) 360. Add this Number, .0101, Part of an Inch, or Rise by Expansion, to the Barometer resting at Inches 25, .19 Tenths, Units under Units, &c. thus: .0101.