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PNEUMATICS.

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748. LET 6 be the capacity of the barrel, “ that of the receiver; then since the defect from the standard altitude has become

h and density cc defect (Vince, Prop. LXVII.)

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we have

h : h a :: density at first : ditto after n turns

:: (2b + r)" : (b + r)" :: 26 +5:6+r:: h : (h a)? and 6 :r:: hă-(ha)ă : 2 (k – a)ă h

749. Let x denote the space through which the elasticity of the air in the tube depresses the mercury; L the length of the tube, h the standard altitude, and a the depth of the air in the tube before inversion; then (Vince's Hyd. Prop. LXI.) we have

h : 2 :: + d-h : a
:. 2 + (l h) x x = ah
and x= -(1 h) ÉN (? h)* + 4ah)

2

one value of which indicates the space through which the air depresses the mercury, and the other the altitude of mercury it would support if placed above it, by its pressure against the top of the tube.

In the problem h = 30
L = 40, and a = 20; ..

x = 7 inches, Hence

h 2 = 224 inches, the altitude required. VOL. II.

2 N

750. Let s be the specific gravity of the air at the Earth's surface, A the area of the given plane, supposed to bear no proportion to the great circle of the earth, and r the radius of the earth; then ns is the weight of a cubic foot of the given uniform medium at the earth's surface, and by the law of gravitation, its weight at the distance

R + x

from the earth's centre is

R?

Xns (R + x) Hence the increment of the pressure or weight of the medium upon the plane is

Rons

(R + x) and that pressure or weight is

X Adx

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81

= 0.

1 Let x = 00. Then

R + x and the pressure required is measured by

nsAR. Hence it appears that the pressure of the infinitely high coluna of any substance whatever is equal to the weight of a column of the same base, and whose altitude is equal to the radius of the earth.

751. Generally, let the compressing force oc (density) c D,

1 and the force of gravity Fc

; required the variation (dist.) 9

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of D.

Let d be the density at the surface of the earth, and R the radius of the earth; then since

R
dCo dQ x F C – Dde x OC also DvaldD

pl
dp = M x Dp-dD

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M being as yet undetermined.

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and its value is that with which this fraction vanishes when for P and D we put R and d. Hence by the rule for estimating such fractions

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752. Let y = d x at be the equation to the DensityCurve, (see Vince's Hyd. p. 82), y representing the density at the distance x from the surface of the earth, and the density at the surface. Then if h be the height of the homogeneous atmosphere, as determined by the barometer, we have (see Vince),

- 1
h =
dy

la which gives

- ydx

aceh

:: y=dxe

(1). Let D be the density of mercury, determined at the time this formula is applied, and b the height at which it then stands in the tube of the barometer; then h : 6::

D and the equation (1) becomes

y = dxe

(2).

1

1

:

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Hence the distance from the surface of the earth of the centre of gravity of the cylinder whose altitude is z, is

Sxydt Jeep da
Jydx

feddi dx

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To verify this result, we should have u = 0, when x = 0. But we then have

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If, however, we find u by the rule for Vanishing Fractions, we have

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753. Let W be the weight of the balloon and all its appendages, d the specific gravity or density of the atmosphere at the surface of the earth when the barometer stands at 6 feet, and

that of the gas. Also let y denote the density of that stratum

whereat the balloon will cease to ascend, and let c be the capacity of the balloon in cubic feet. Then since the weight of the air displaced by the gas is

с ху

and that of the balloon, its appendages and gas, is

W+cx

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n

:: by the question (Vince. Prop. XIV.)

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5

Ex. 1. Let the gas be hydrogen, or n = 13; b = 30 inches = feet; D = 14019 (water being supposed to have the density

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Let it further be supposed that W = 20 stone = 4480 ounces, and c3 = 200000 cubic feet. Then

156000 X = 42057 X I.

14912

4875 = 42057 x l.

466

= 42057 x 2.34768 feet nearly. See Barlow's Tables. .. x = 98736 feet

- 32912 yards

= 18 miles 1232 yards. This prodigious altitude is owing to the disproportion of the balloon to the weight of the load and materials. The surface of such a machine, even under the form of a sphere, is about 24000 square feet, and the weight of that surface would consequently be considerably greater than the weight here attributed to it.

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