ON IIEAT AS A MODE OF MOTION. 
Ill 
At the present time it seems to be fashionable to make pharmaceutical prepa¬ 
rations as condensed as possible ; but it must be remembered that in these multum 
in parvo preparations accidental impurities are concentrated as well as remedial 
principles, and we too often find that preparations of this class form but very 
imperfect substitutes for those they are intended to represent, to the disappoint¬ 
ment both of the prescriber and the patient. 
Albinus John Roberts. 
18, Conduit Street , IF., loth August , 1863. 
TYNDALL ON- IIEAT AS A MODE OF MOTION. 
ABSTRACT OF THE THEORY. 
BY MB. JOSEPH INCE. 
During the season of 1862, Professor Tyndall delivered a course of twelve lec¬ 
tures on Heat, at the Royal Institution : the theory propounded, and the manner 
in which it was illustrated, have subsequently excited considerable attention. 
In the hope of placing some of the main bearings of the subject in a concise and 
intelligible form, the following abstract has been attempted. It will be felt 
that what is termed a Review would scarcely escape censure as an impertinence 
even by those who have confidence in that most superficial and unsatisfactory 
style of literature. In the present sketch, there is not one thought, although 
presented in a different dress, that is not directly taken from the lecturer’s own 
work. 
Lord Bacon, like every other great man, was far in advance of the age in 
which he lived; it seems also that he was in advance of ours, for thus he speaks 
in the twentieth aphorism of the second book of the ‘ Novum Organum—“ When 
I say of motion, that is the genus of which heat is a species, I would be understood 
to mean, not that heat generates motion or that motion generates heat (though 
both are true in certain cases), but that heat itself, its essence and quiddity, is mo¬ 
tion and nothing else ; limited, however, by the specific differences which I will 
presently subjoin, as soon as I have added a few cautions for the sake of avoid¬ 
ing ambiguity. Nor again, must the communication of heat, or its transitive 
nature, by means of which a body becomes hot when a hot body is applied to it, 
be confounded with the form of heat. For heat is one thing, and heating is 
another. Heat is produced by the motion of attrition without any preceding- 
heat. Heat is an expansive motion, whereby a body strives to dilate and stretch 
itself to a larger sphere or dimension than it had previously occupied. This dif¬ 
ference is most observable in flame, where the smoke or thick vapour manifestly 
dilates and expands into flame. It is shown also in all boiling liquid, which 
manifestly swells, rises, and bubbles, and carries on the process of self-expansion, 
till it turns into a body far more extended and dilated than the liquid itself, 
namely, into vapour, smoke, or air. 
“ The third specific difference is this, that heat is a motion of expansion, not 
uniformly of the whole body together, but in the smaller parts of it; and at the 
same time checked, repelled, and beaten back, so that the body acquires a motion 
alternative, perpetually quivering, striving and struggling, and irritated by 
repercussion, whence springs the fury of fire and heat. Again, it is shown in 
this, that when the air is expanded in a calender glass, without impediment or 
repulsion, that is to say uniformly and equably, there is no perceptible heat. 
Also when wind escapes from confinement, although it bursts forth with the 
greatest violence, there is no very great heat perceptible; because the motion is 
of the whole, without a motion alternating in the particles. 
