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it) when Professor Tyndall composed during a summer holiday, 
and subsequently delivered at the meeting of the British 
Association at Liverpool in 1870, his celebrated discourse on 
the “ Use of the Imagination in Science.” I heard that 
o 
eloquent discourse, and I considered at the time that many of 
the instances adduced from the mathematical sciences were 
legitimate deductions from established premisses, and implied 
no use of the imagination properly so called. There has, how- 
ever, been abundant use made of it since that time, both by 
the lecturer himself and by others, and I think a note of 
warning on this head is not out of place. 
As this almost concludes the introductory portion of the 
Address, I will make a passing allusion to Canon Birks’ 
paper on the errors and confusion which have been made 
in dynamical science, partly by new nomenclature, and partly 
by a misunderstanding, by some scientists of high pre- 
tensions, of the ordinary principles of mechanical science. 
Change of nomenclature is generally attended with some 
inconvenience, though in some of the instances produced by 
Professor Birks the change has been made by two of the most 
accomplished mathematicians and physicists of the day, 
namely by Sir William Thomson and Professor Tait, in their 
excellent treatise on Natural Philosophy. An old mathema- 
tician like myself finds some little repugnance to part with his 
friend vis viva , and to find it again under the designation kinetic 
energy ; but new nomenclature would be a trifling matter if 
it had not introduced confusion into the ideas of some dis- 
tinguished men of science. It must be borne in mind that, 
with regard to the science of pure dynamics, no new mechanical 
principle whatever has been discovered, and that the laws of 
conservation and dissipation of energy (even when applied to 
the universe or cosmos) must be applied in the same way as 
they would have been forty years ago, though with greater 
analytical resources, presuming that we have data enough to 
solve any particular problem presented to us. With regard 
however to the conversion of energy of one kind into 
energy of another, as occurs in the notable instance of heat 
into motion, or the effects of motion into heat, so that not a 
particle of either matter or force is wasted throughout the 
universe ; this is a most important discovery of tho present 
epoch, though I do not know that religion is immediately 
concerned with it. 
With these preliminary remarks I will proceed to introduce 
the several topics which I intend to form the principal subject- 
matter of this Address. 
