TEANSACTIONS OF THE SECTIONS. 



Section A.— MATHEMATICAL AND PHYSICAL SCIENCE. 



Pkesident of the Section — 



Professor Sir William Thomson, M.A., LL.D., D.C.L., F.R.S.L.and E. 



THURSDAY, SEPTEMBER 1. 



The President delivered the following Address : — 



■On the Sources of Energy in Nature available to Man for the Production of 



Mechanical Effect. 



During the fifty years' life of the British Association, the Advancement of Science 

 for which it has lived and worked so well has not been more marked in any 

 department than in one which belongs very decidedly to the Mathematical and 

 Physical Section — the science of Energy. The very name energy, thouo-h first 

 used in its present sense by Dr. Thomas Young about the beginning of this cen- 

 tury, has only come into use practically after the doctrine which defines it had 

 during the first half of the British Association's life, been raised from a mere 

 formula of mathematical dynamics to the position it now holds of a principle 

 pervading all nature and guiding the investigator in every field of science. 



A little article communicated to the Royal Society of Edinburo-h a short 

 time before the commencement of the epoch of energy under the title ' On the 

 Sources Available to Man for the Production of Mechanical Effect ' ' contained the 

 -following : — 



' Men can obtain mechanical effect for their own purposes by working mechani- 

 cally themselves, and directing other animals to work for them, or by usino- natural 

 heat, the gravitation of descending solid masses, the natural motions of water and 

 air, and the heat, or galvanic currents, or other mechanical effects produced bv 

 •chemical combination, but in no other way at present known. Hence the stores 

 from which mechanical effect may be drawn by man belong to one or other of 

 the following classes : — 

 ' I. The food of animals. 

 ' II. Natural heat. 



' III. Solid matter found in elevated positions, 

 ' IV. The natural motions of water and air. 



' V. Natural combustibles (as wood, coal, coal-gas, oils, marsh-gas, diamond, 

 native sulphur, native metals, meteoric iron). 



'VI. Artificial combustibles (as smelted or electrically-deposited metals, 

 hydrogen, phosphorus). 



'In the present communication, known facts in natural history and physical 

 science, with reference to the sources from which these stores have derived their 

 mechanical energies, are adduced to establish the following general con- 

 •clusions : — 



'1. Heat radiated from the sun (sunlight being included in this term) is the 

 principal source of mechanical effect available to man.'- From it is derived the whole 



' Read at the Koyal Society of Edinburgh on February 2, 1852 (^Proceedings of 

 that date). 



* A general conclusion equivalent to this was published by Sir John Herschel in. 

 1833. See his Astronomy, edit. 1819, § (399). 



1881. L L 



