justifying, in the eyes of any one, such a course of conduct.

As Professors of Natural Philosophy we have one sad remark to make. The great majority of our critics have exhibited almost absolute ignorance as to the proper use of the term Force, which has had one, and only one, definite scientific sense since the publication of the Principia. As such men are usually among the exceptionally well educated, ignorance of this important question must be all but universal. In addition to what we have said on the subject in the text (§ 97), we would now only mention that the sole recorded case of true Persistency or Indestructibility of Force which we recollect having ever met with, occurs in connection with Baron Munchausen's remarkable descent from the moon. It is, no doubt, a very striking case; but it is apparently unique, and it was not subjected to scientific scrutiny.

B. STEWART.

NTRODUC

Best of the B

ters

The abode

Italming

P. G. TAIT.

Application of this principle to Christian miracles—
Erroneous position of old divines,

Such opposed to the genius of Christianity,
New method of explanation,

Application of this principle to the doctrines of the extreme
scientific school-

The visible universe will probably come to an end in
transformable energy,

It must have been developed out of the invisible,

7

83-84

85

86

87

96

Definition of the term 'Physical Universe,'

It contains something else besides matter or stuff,
Grounds of our belief in an external universe,

These in accordance with our definition of the laws of

the universe (Art. 54),

95

102

Meaning of conservation,

96 103

Newton's second interpretation of his Third Law, .

Friction changes work into heat,

Historical sketch of the theory of energy,

Transformability of energy constitutes its use,

Case where energy is useless,

Historical Sketch of Second Law of Thermodynamus—

*Carnot's perfect heat-engine,

*Sir W. Thomson's definition of absolute temperature,
*Melting point of ice lowered by pressure,
*Sir W. Thomson's rectification of Carnot's reason-

105 116

*106 117

*107 118

*108 120

120

*109-*110
*III-*113 122

114 126

Past of the physical universe,

CHAPTER IV.

MATTER AND ETHER.

Inquiry regarding structure and material of the universe,

Various hypotheses regarding matter

(1.) Greek notion of the Atom,

Speculations of Lucretius,

(2.) Theory of Boscovich (centres of force),
(3.) Theory of infinite divisibility, .

(4.) Vortex-atom theory,

Remarks on these theories,

Relative quantity of matter associated with energy,

Universal gravitation—

Is a weak force,