Auc: 20, 1874 J 



NATURE 



'id'i 



But the main feature of the volume is that from which 

 it takes its name, the essay on the Correlation of 

 Physical Forces, the views contained in which were first 

 advanced in a lecture at the London Institution in 

 January 1842, printed by the proprietors, and subsequently 

 more fully developed in a course of lectures in 1843, pub- 

 lished in abstract in the Literary Gazette. This essay 

 has a vahte peculiar to itself. Though it has long ago 

 accomplished the main point of its scientific mission to 

 the world, it will always retain its place in the memory of 

 the student of human thought, as one of the documents 

 which serve for the construction of the history of science. 



It is not by discoveries only, and the registration of them 

 by learned societies, that science is advanced. The true 

 seat of science is not in the volume of Transactions, but in 

 the living mind, and the advancement of science consists 

 in the direction of men's minds into a scientific channel ; 

 whether this is done by the announcement of a dis- 

 covery, the assertion of a paradox, the invention of a 

 scientific phrase, or the exposition of a system of doctrine. 

 It is for the historian of science to determine the magni- 

 tude and direction of the impulse communicated by either 

 of these means to human thought. 



But what we require at any given epoch for the ad- 

 vancement of science is not merely to set men thinking, 

 but to produce a concentration of thought in that part of 

 the field of science which at that particular season ought 

 to be cultivated. In the history of science we find that 

 effects of this kind have often been produced by sugges- 

 tive books, which put into a definite, intelligible, and 

 communicable form, the guiding ideas that are already 

 working in the minds of men of science, so as to lead 

 them to discoveries, but which they cannot yet shape into 

 a definite statement. 



In the first half of the present century, when what is 

 now called the principle of the conservation of energy was 

 as yet unknown by name, it " flung its vague shadow back 

 from the depths of futurity," and those who had greater 

 or less understanding of the times sketched out with 

 greater or less clcnrness their view of the form into which 

 science was shaping itself. 



Some of these addressed themselves to the advanced 

 cultivators of science, speaking, of course, in learned 

 phraseology ; but others appealed to a larger audience, 

 and spoke in language which they could understand. 

 Mrs. Somerville's bookon the "Connection of the Physical 

 Sciences" was published in 1S34 and had reached its 

 eighth edition in 1849. This fact is enough to show that 

 there already existed a widespread desire to be able to 

 form some notion of physical science as a whole. 



But when we examine her book in order to find out the 

 nature of the connection of the physioal sciences, we are 

 at first tempted to suppose that it is due to the an 

 of the bookbinder, who has bound into one volume 

 such a quantity of information about each] of them. 

 What we find in fact is a series of expositions of 

 different sciences, but hardly a word about their connec- 

 tion. The little that is said about this connection has 

 reference to the mutual dependence of the different 

 sciences on each other, a knowledge of the elements of 

 one being essential to the successful piosecution of 

 another. Thus physical astronomy requires a knowledge 

 of dynamics, and the practical astronomer must learn a 



certain amount of optics in order to understand atmo- 

 spheric refraction and the adjustment of telescopes. The 

 sciences are also shown to have a common method, 

 namely mathematical analysis ; so that analytical methods 

 invented for the investigation of one science are 'often 

 useful in another. 



The unity shadowed forth in Mrs. Somerville's book 15 

 therefore a unity of the method of science, not a unity of 

 the processes of nature. 



Sir W. Grove's essay may be fairly called a popular 

 book, as it has reached its sixth edition. It is, there- 

 fore, not merely a record of the speculations of the 

 author, but an index of the state of scientific thought 

 among a large number of readers. It has not the universal 

 facility and occasional felicity of exposition which distin- 

 guish Mrs. Somerville's writings. No one could use it as 

 a text-book of any science, or even as an aid to the culti- 

 vatioft of the art of scientific conversation. The design 

 of the book is to show that of the various forms of energy 

 existing in nature, any one may be transformed into any 

 other, the one form appearing as the other disappears. 

 This is w hat is meant in the essay by the '"' correlation of 

 the physical forces," and the whole essay is an exposition 

 of this fact, each of the physical forces in turn being taken 

 as the starting-point, and employed as the source of all 

 the others. 



We are sorry that we are not at present able to refer to 

 the early reviews of the essay as indic^rting the reception 

 given to the doctrine by the literary and scientific public 

 at the time of its original publication. It has eeffatnly 

 exercised a very considerable effect in moukting the toass 

 of what is called scientific opinion, that is to say the in- 

 fluence which determines what a scientific man shall say 

 vihen he has to make a statement about a science which 

 he does not understand. Many things in the essay 

 which were then considered contrary to scientific opinion, 

 and were therefore objected to, have since then become 

 themselves part of scientific opinion, so that the objec- 

 tions now appear unintelligible to the rising generation of 

 the scientific public. 



Helmholtz's essay " On the Conservation of Force," 

 published ia 1847, undoubtedly masters a far gi'eater step 

 in science, but the immediate influence was confined to a 

 small number of trained men of science, and it had little 

 direct effect on the public mind. 



The various papers of Mayer contain matter calculated 

 to awaken an interest in the transformation of energy 

 even in persons not' exclusively devoted to science, but 

 they were long unknown in this country, and produced 

 little direct effect, even in Germany, at the time of their 

 publication. 



The rapid development of thermodynamics, and of 

 other applications of the principle of the conservation of 

 energy, at the beginning of the second half of this century, 

 belongs to a later stage of the history of science than that 

 with which we have to do. 



To form a just estimate of the value of Sir W. Grove's 

 work we must regard it as the instrument by which certain 

 scientific ideas were diffused over a large area, in lan- 

 guage sufficiently appropriate to prevent misapprehen- 

 sion, and yet sufficiently familiar to be listened to by 

 persons who would recoil with horror from any statement 

 in which literary convention is sacrificed to precision. 



