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ART.

PAGE

to the cosine of the angle which its direction makes with the normal to
the surface. Divers remarks, and considerations on the object and extent
of thermological problems, and on the relations of general analysis with
the study of nature.

22

.

GENERAL NOTIONS AND PRELIMINARY DEFINITIONS.

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22-24. Permanent temperature, thermometer. The temperature denoted

by 0 is that of melting ice. The temperature of water boiling in a

given vessel under a given pressure is denoted by 1 .

25. The unit which serves to measure quantities of heat, is the heat

required to liquify a certain mass of ice

26. Specific capacity for heat .

27–29. Temperatures measured by increments of volume or by the addi.

tional quantities of heat. Those cases only are here considered, in which

the increments of volume are proportional to the increments of the

quantity of heat. This condition does not in general exist in liquids ;

it is sensibly true for solid bodies whose temperatures differ very much

from those which cause the change of state

30. Notion of external conducibility

31. We may at first regard the quantity of heat lost as proportional to the

temperature. This proposition is not sensibly true except for certain

limits of temperature

32–35. The heat lost into the medium consists of several parts. The effect

is compound and variable. Luminous heat

36. Measure of the external conducibility

37. Notion of the conducibility proper. This property also may be observed

in liquids .

38, 39. Equilibrium of temperatures. The effect is independent of contact .

40–49. First notions of radiant heat, and of the equilibrium which is

established in spaces void of air ; of the cause of the reflection of rays
of heat, or of their retention in bodies; of the mode of communication
between the internal molecules; of the law which regulates the inten.
sity of the rays emitted. The law is not disturbed by the reflection of

heat.

50, 51. First notion of the effects of reflected heat

52–56. Remarks on the statical or dynamical properties of heat. It is the

principle of elasticity. The elastic force of aeriform fluids exactly indi-

cates their temperatures

ib.

37

57–59. When two molecules of the same solid are extremely near and at

unequal temperatures, the most heated molecule communicates to that
which is less heated a quantity of heat exactly expressed by the product
of the duration of the instant, of the extremely small difference of the
temperatures, and of a certain function of the distance of the molecules .

41

60. When a heated body is placed in an aeriform medium at a lower tem.

perature, it loses at each instant a quantity of heat which may be
regarded in the first researches as proportional to the excess of the

temperature of the surface over the temperature of the medium

61—64. The propositions enunciated in the two preceding articles are founded

on divers observations. The primary object of the theory is to discover

all the exact consequences of these propositions. We can then measure

the variations of the coefficients, by comparing the results of calculation

with very exact experiments

.

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LAW OF THE PERMANENT TEMPERATURES IN A PRISM OF SMALL THICKNESS.

SECTION VI.

THE HEATING OF CLOSED SPACES.

81–84. The final state of the solid boundary which encloses the space

heated by a surface b, maintained at the temperature a, is expressed by

the following equation :

P

m -- n=(a − n)

1+P

The value of P is

ge 9

+ + )

Н

K

m is the temperature of the internal

air, n the temperature of the external air, g, h, H measure respectively
the penetrability of the heated surface o, that of the inner surface of the
boundary s, and that of the external surface 8; e is the thickness of the

boundary, and K its conducibility proper .

85, 86. Remarkable consequences of the preceding equation .

87–91. Measure of the quantity of heat requisite to retain at a constant

temperature a body whose surface is protected from the external air by

62

65

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85

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