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to the demonstrated conclusion. He illustrates it by the rela- 
tions of heat to mechanical work and their mutual interchange, 
in examples with which the readers of his other essays and 
lectures are entirely familiar. He considers next the analogous 
interchange of decomposition and combustion in the use of the 
galvanic battery for chemical results — illustrating by several 
examples the truth that chemical elements, say hydrogen and 
oxygen, which are united in combustion at one point in the 
circuit, are liberated in exact equivalents at the other. Having 
taken two steps in his argument, he essays a third, and sug- 
gests that the same process under similar laws may go on in 
the body of man. Having demonstrated that heat is inter- 
changeable backwards and forwards with mechanical energy 
in mathematical equivalents, and that combustion involving 
heat is in like manner interchangeable with chemical decom- 
positions, he abruptly asks : “ Is the animal body then to be 
classed among machines ? ” The friction wheel or the galvanic 
battery only distributes force — transferring it from one point to 
another, and varying its manifestations to the senses — but 
never creating it. Does the animal body do anything more ? 
“ When I lift a weight, or throw a stone, or climb a mountain, 
or wrestle with my comrade, am I not conscious of actually 
creating and expending force ?” The ingenuity of thus put- 
ting his case is altogether admirable. It is as though he had 
said : the question whether the body is or is not a machine 
must be decided by the question whether it is capable of gene- 
rating muscular or mechanical energy. The man who asserts 
that it only transfers force must own that it is a machine — 
the man who denies that it is a machine must hold that it 
can of itself generate, i.e., originate, muscular force. The 
tyro in logic would recognize the possible fallacy which may 
lie in the major premise of Prof. Tyndall’s disjunctive syllogism. 
Even did he know little about the subject matter, he might at 
least be wary enough to say : I am not prepared to say that A 
is either B or C, for it may possibly be either B, C, or C + D. 
That is, the human body may be something else than either 
a generator or a transmuter of force — it may perhaps per- 
form other offices than a friction wheel or a galvanic battery. 
Whether Prof. Tyndall does not himself concede this a little 
further on, we shall ask in due time. But Prof. Tyndall having 
shaped his major premise to suit himself, proceeds to discuss 
the minor premise by asking whether the human body origi- 
nates, i.e., generates, mechanical force. He answers his own 
question by an elaborate and varied series of illustrations, all 
of which are designed to show that mechanical foi’co and heat 
and chemism (chemical attraction) are related to one another in 
