TRANSACTIONS OF SECTION G. 767 



Section G.— MECHANICAL SCIENCE. 

 President op the Section'— Sir W. Aemsteoxg, C.B., D.C.L., LL.D., F.R.S. 



THURSDAY, SEPTEMBER 1. 



The Pbesident delivered the following Address : — 



The astonishing progress which has heen made in the construction and applica- 

 tion of machinery during the half-century which has elapsed since the nativity of 

 the British Association for the Advancement of Science, is a theme which I might 

 with much complacency adopt in this address ; hut instead of reviewing the past 

 and exulting in our successes, it will he more profitahle to look to the future, and 

 to dwell on our failures. It is but justice to say that by growing experience, by 

 increased facilities of manufactiu-e, and by the exercise of much skill and ingenuity, 

 we have succeeded in multiplying and expanding the applications of ovu- chief 

 motor, the Steam Engine, to an extent that would have appeared incredible fifty 

 years ago, but the gratulation inspired by this success is clouded by the reflection 

 that the steam engine even in its best form remains to this day a most wasteful 

 apparatus for converting the energy of heat into motive power. Our predecessors 

 of that period had not the advantage of the knowledge which we possess of the 

 true nature of heat, and the conditions and limits affecting its utilization. In their 

 time heat was almost universally regarded as a fluid which, under the name of 

 caloric, was supposed to lie dormant in the interstices of matter until forced out 

 by chemical or mechanical means. Although Bacon, Newton, Cavendish, and 

 Boyle all maintained that heat was only internal motion, and although Davy and 

 Eumford not only held that view but proved its accuracy by experiment, yet the 

 old notion of caloric continued to hold its ground, until in more recent times, 

 Joule, Meyer, Codling, and others put an end to all doubt on the subject, and 

 established the all-important fact that heat is a mode of motion having, like any 

 other kind of motion, its exact equivalent in terms of work. By their reasonings 

 and experiments it has been definitely proved that the quantity of heat which 

 raises the temperature of a pound of water 1° Fahrenheit, has a mechanical value 

 equal to lifting 772 lbs. one foot high, and that conversely the descent of that 

 weight from that height is capable of exactly reproducing the heat expended. 



The mechanical theory of heat is now universally accepted, although a remnant 

 of the old doctrine is displayed in the continued use of the misleading term 'latent 

 heat.' According to the new theory, heat is an internal motion of molecules 

 capable of being communicated from the molecules of one body to those of another, 

 the result of the imparted motion being either an increase of temperature, or the 

 performance of work. The work may be either external, as where heat, in expand- 

 ing a gas, pushes away a resisting body, or it may be internal, as where heat pidls 

 asunder the cohering particles of ice in the process of liquefaction, or it may Ije 

 partly internal and partly external, as it is in the steam engine, where the 'first 

 efi'ect of the heat is to separate the particles of water into vapour, and the second 

 to give motion to the piston. Internal as well as external work may be reconverted 

 into heat, but until the reconversion takes place the heat which did the work does 

 not exist as Heat, and it is delusive to call it 'latent heat.' All heat problems are 



