September 12, 1901] 



NA TURE 



471 



tion is passing through a transitional stage. The recent debates in 

 Parliament ; the great gifts of Mr. Carnegie ; the discussion as to 

 University organisation in the North of England ; the reconsti- 

 tution of the University of London ; the increasing importance 

 attached to the application of knowledge both to the investiga- 

 tion of Nature and to the purposes of industry, are all evidence 

 of the growing conviction that without advance in education we 

 cannot retain our position among the nations of the world. If 

 the British Association can provide a platform on which these 

 matters may be discussed in a .scientific but practical spirit, free 

 from the misrepresentations of the hustings and the exaggerations 

 of the partisan, it will contribute in no slight measure to the 

 national welfare. 



But amid the old and new activities of our meeting the under- 

 tone of sadness, which is never absent from such gatherings, 

 will be painfully apparent to many of us at Glasgow. The life- 

 work of Prof. Tait has ended amid the gloom of the war-cloud. 

 A bullet, fired thousands of miles away, struck him to the heart, 

 so that in their deaths the father and the brave son, whom he 

 loved so well, were not long divided. Within the last year, too, 

 America has lost Rowland ; Viriamu Jones, who did yeoman's 

 service for education and for science, has succumbed to a long 

 and painful illness ; and one who last year at Bradford seconded 

 the proposal that I should be your President at Glasgow, and 

 who would unquestionably have occupied this Chair before 

 long had he been spared to do so, has une.xpectedly been called 

 away. A few months ago we had no reason to doubt that 

 George Francis FitzGerald had many years of health and work 

 before him. He had gained in a remarkable way not only the 

 admiration of the scientific world, but the affection of his 

 friends, and we shall miss sadly one whom we all cared for, and 

 who, we hoped, might yet add largely to the achievements which 

 had made him famous. 



The Science of the Nineteenth Century. 



Turning from these sad thoughts to the retrospect of the cen- 

 tury which has so lately ended, I have found it to be impossible to 

 free myself from the influence of the moment and to avoid, even 

 if it were desirable to avoid, the inclination to look backward 

 from the standpoint of to-day. 



Two years ago Sir Michael Foster dealt with the work of the 

 century as a whole. Last year Sir William Turner discussed in 

 greater detail the growth of a single branch of science. A third 

 and humbler task remains, viz., to fix our attention on some of 

 the hypotheses and assumptions on which the fabric of modern 

 theoretical science has been built, and to inquire whether the 

 foundations have been so " well and truly " laid that they may 

 be trusted to sustain the mighty superstructure which is being 

 raised upon them. 



The moment is opportune. The three chief conceptions 

 which for many years have dominated physical as distinct from 

 biological science have been the theories of the existence of 

 atoms, of the mechanical nature of heat, and of the existence 

 of the ether. 



Dalton's atomic theory was first given to the world by a 

 Glasgow professor — Thomas Thomson — in the year 1S07, 

 Dalton having communicated it to him In 1804. Rumford'sand 

 Davy's experiments on the nature of heat were published in 

 1798 and 1799 respectively ; and the celebrated Bakerian 

 Lecture, in which Thomas Young established the undulatory 

 theory by explaining the interference of light, appeared in the 

 Philoiophical Transactions in 1801. The keynotes of the 

 physical science of the nineteenth century were thus struck, as 

 the century began, by four of our fellow-countrymen, one of 

 whom — Sir Benjamin Thompson, Count Rumford — preferred 

 exile from the land of his birth to the loss of his birthright as a 

 British citizen. 



Doubts as to Hcientific Theories. 



It is well known that of late doubts have arisen as to whether 

 the atomic theory, with which the mechanical theory of heat is 

 closely bound up, and the theory of the existence of an ether 

 have not served their purpose, and whether the time has not 

 come to reconsider them. 



The facts that Prof. Poincare, addressing a congress of 

 physicists in Paris, and Prof. Poynting, addressing the Physical 

 Section of the Association, have recently discus.sed the true 

 meaning of our scientific methods of interpretation ; that Dr. 

 James Ward has lately delivered an attack of great power on 

 many positions which eminent scientific men have occupied ; and 



NO. 1663, VOL. 64] 



that the approaching end of the nineteenth century led Prof. 

 Haeckel to define in a more popular manner his own very definite 

 views as to the solution of the " Riddle of the Universe," 

 are perhaps a sufficient justification of an attempt to lay 

 before you the difficulties which surround some of these 

 questions. 



To keep the discussion within reasonable limits, I shall illus- 

 trate the principles under review by means of the atomic theory, 

 with comparatively little reference to the ether, and we may also 

 at first confine our attention to inanimate objects. 



The Construction of a Model of Nature. 

 A natural philosopher, to use the old phrase, even if only 

 possessed of the most superficial knowledge, would attempt to 

 bring some order into the results of his observation of Nature by 

 grouping together statements with regard to phenomena which 

 are obviously related. The aim of modern science goes far 

 beyond this. It not only shows that many phenomena are re- 

 lated which at first sight have little or nothing in common, but, 

 in so doing, also attempts to explain the relationship. 



Without spending time on a discussion of the meaning of the 

 word " explanation," it is sufficient to say that our efforts to es- 

 tablish relationships between phenomena often take the form ol 

 attempting to prove that, if a limited number of assumptions are 

 granted as to the constitution of matter, or as to the existence of 

 quasi-material entities, such as caloric, electricity, and the ether, a 

 wide range of observed facts falls into order as a necessary con- 

 sequence of the assumptions. The question at issue is whether 

 the hypotheses which are at the base of the scientific theories 

 now most generally accepted are to be regarded as accurate 

 descriptions of the constitution of the universe around us, or 

 merely as convenient fictions. 



Convenient fictions be it observed, for even if they are fictions 

 they are not useless. From the practical point of view it is a 

 matter of secondary importance whether our theories and as- 

 sumptions are correct, if only they guide us to results which are 

 in accord with facts. The whole fabric of scientific theory may 

 be regarded merely as a gigantic " aid to memory " ; as a means 

 for producing apparent order out of disorder by codifying the 

 observed facts and laws in accordance with an artificial system, 

 and thus arranging our knowledge under a comparatively small 

 number of heads. The simplification introduced by a scheme 

 which, however imperfect it may be, enables us to argue from a 

 few first principles, makes theories of practical use. By means 

 of them we can foresee the results of combinations of causes 

 which would otherwise elude us. We can predict future events, 

 and can even attempt to argue back from the present to the un- 

 known past. 



But it is possible that these advantages might be attained by 

 means of axioms, assumptions, and theories based on very false 

 ideas. A person who thought that a river was really a streak of 

 blue paint might learn as much about its direction from a map 

 as one who knew it as it is. It is thus conceivable that we 

 might be able, not indeed to construct, but to imagine, some- 

 thing more than a mere map or diagram, something which might 

 even be called a working model of inanimate objects, which was 

 nevertheless very unlike the realities of Nature. Of course, the 

 agreement between the action of the model and the behaviour 

 of the things it was designed to represent would probably be 

 imperfect, unless the one were a facsimile of the other ; but it is 

 conceivable that the correlation of natural phenomena could be 

 imitated, with a large measure of success, by means of an 

 imaginary machine, which shared with a map or diagram the 

 characteristic that it was in many ways unlike the things it re- 

 presented, but might be compared to a model in that the behaviour 

 of the things represented could be predicted from that of the 

 corresponding parts of the machine. 



We might even go a step further. If the laws of the working 

 of the model could be expressed by abstractions, as, for exatrlple, 

 by mathematical formula;, then, when the formulae were ob- 

 tained, the model might be discarded, as probably unlike that 

 which it was made to imitate, as a mere aid in the construction 

 of equations, to be thrown aside when the perfect structure of 

 mathematical symbols was erected. 



If this course were adopted, we should have given up the at- 

 tempt to know more of the nature of the objects which surround 

 us than can be gained by direct observation, but might never- 

 theless have learned how these objects would behave under given 

 circumstances. 



We should have abandoned the hope of a physical explanation 



