* 3 8

P N E U M A T I C 8.

at the Height of seven Miles than at ^Earth’s Surface; and therefore at thetitudes of 7. 14. 21. 28. 35. 42. 49. $ C 'the Rarity of the Air will be 4. 16. 64 *256. 1204. 4096. 16384. &c.

If the Air were of an equal Denfi^throughout, the Height of the Atmosph^

Ml/

ful Instruments and - Machines, some of which I ^exhibit here, and others in the Sequel of this Wot <4^8. We have strewn in the last Annotation that ,jjPressure of the Air, in its State of Mean Gravity, y jsupport a Column of Quicksilver to the Altitude ofInches; and (in Annot. LXlII.) it was, shewn that { ‘ 5specific Gravity of Mercury was to that of Water? J14 to 1 nearly; therefore the said Mean Presfurf 0 (Air will sustain a Column of Water to the Pleigjl c c14X29,5 = 413 Inches = 34 Feet 5 Inches. But Qq;Mercury is not quite 14 Times as heavy as Water, ,may take 400 Inches for the Measure of the Mean ^,1vity of the Air on Water and 29,5 for Mercury; and t ^we shall have D C : D E :: P : 29,5 in Mercury WD C : DE :: P : 400, in Water; consequently 40O

= DEXP.

9. Aga

of

m, let the Standard Altitude of MercysWater be 11=29,5 or 400, and let the Altitude f - 0 (iA; then will P = FI4 and then the above E^Adwill give this Analogy : As S : r H-fT : H, ^

S : S — s :: PI: or DE : E C :: H : h\ consecssfi^Fby having DE or C E given, you know the An .(iih— F G. Thus for Example : Let DC = iOit is reqtiired to find what Altitude of Water I 1 Q$by its Pressure raise the Surface at C one Inch ? IEA . h= 1, DE = g, and H=400 : Then DE : CE --that is, 9 : 1 ;; 400 : 44,4; or F 6=44^ Inches 1 ^]y, or 3 Feet 8;- Inches. Thus again, Querytitude F G that shall raise the Surface C 9 Inch^y^ dof the Whole ? Say, As 1 : 9 :: 400 : 3600=1 J e <)300 Feet. Thus the Altitudes are found D r 41Ktenth Part of the whole Soace D C, as in the f° xi °

Table.