of Edinburgh, Session 1862-63. 121 
Fifteenth Annual Report of the Regents of the University of the 
State of New York on the Condition of the State Cabinet of 
Natural History. 8vo. — From the same. 
Scheikundige Yerhandelingen en Onderzoekingen uitgegeven door 
Gr. J. Mulder. Derde Deel. Tweede Stuk. 8vo. — From 
the Author. 
Monday, 20th April 1863. 
Principal FOKBES, Vice-President, in the Chair. 
The following Communications were read : — - 
1. On the Conservation of Energy. By Professor Tait. 
(Abstract.) 
{This Lecture was given at the reguest of the Council.') 
What Matter or Force may be, we have not as yet the slightest 
idea. Matter is only known to us by the forces it exerts or resists. 
It is possible that there may be hut one species of ultimate parts 
(molecules or atoms ?) of matter ; but in the present state of chemical 
science, it is more philosophical to reason as if the ultimate parts 
of the various elementary bodies are distinct. However this may 
be, a particle of hydrogen, oxygen, sodium, or gold, exerts certain 
definite forces upon other particles ; which forces, we have every 
reason to believe, will remain for ever unchanged, unless the so- 
called element should at some future time be decomposed. 
Now, for such elementary particles, change of position (grouping) 
or motion (relative) is the only affection we can conceive ; and we 
must endeavour to deduce, from the relation between forces and the 
motions they produce, all the phenomena of nature, except perhaps 
some of those exhibited in living structures. 
All that is necessary for such an inquiry has been most distinctly 
laid down by Newton in his Axiom ata, and the Scholia appended 
to them. A brief resume of what Newton has there done will lead 
us easily and naturally to the Conservation of Energy — though 
stated for visible motions only, and without reference to the ener- 
*gies of heat, electricity, &c. 
