52o POPULAR SCIENCE MONTHLY. 



The world remains a more wonderful place than ever; we may be sure 

 that it abounds in riches not yet dreamed of; and although we can not 

 hope ever to explore its innermost recesses, we may be confident that 

 it will supply tasks in abundance for the scientific mind for ages to 

 come. 



One significant result of the modern tendency is that we no longer 

 with the same obstinacy demand a mechanical explanation of the phe- 

 nomena of light and electricity, especially since it has been made clear 

 that, if one mechanical explanation is possible, tbere will be an infinity 

 of others. Some minds, indeed, reveling in their new-found freedom, 

 have attempted to disestablish ordinary or 'vulgar' matter altogether. 

 J may refer to a certain treatise which, by some accident, does not bear 

 its proper title of ' yKlher and no Matter,' and to the elaborate investi- 

 gations of Professor Osborne Reynolds, which present the same pecu- 

 liarity, although the basis is different. Speculations of this nature 

 have, however, been so recently and (if I may say it) so brilliantly 

 dealt with by Professor Poynting before this section that there is little 

 excuse for dwelling further on them now. I will only advert to the 

 question whether, as some suggest, physical science should definitely 

 abandon the attempt to construct mechanical theories in the older 

 sense. The question would appear to be very similar to this, whether 

 we should abandon the use of graphical methods in analysis. In either 

 ease we run the risk of introducing extraneous elements, possibly of a 

 misleading character; but the gain in vividness of perception and in 

 suggest iveness is so great that we are not likely altogether to forego 

 it, by excess of prudence, in one case more than in the other. 



We have traveled some distance from Stokes and the mathematical 

 physics of half a century ago. May I add a few observations which 

 might perhaps have claimed his sympathy? They are in substance 

 anything but new, although I do not find them easy to express. We 

 have most of us frankly adopted the empirical altitude in physical 

 science; it has justified itself abundantly in the past, and has more and 

 more forced itself upon us. We have given up the notion of causa- 

 tion, except as a convenient phrase; what were once called laws of na- 

 ture are now simply rules by which we can tell more or less accurately 

 what will be the consequences of a given state of things. We can not 

 help asking, How is it that such rules are possible? A rule is invented 

 in the first instance to sum up in a compact form a number of past 

 experiences; but we apply it with little hesitation, and generally with 

 success, to the prediction of new and sometimes strange ones. Thus 

 the law of gravitation indicates the existence of Neptune; and Pres- 

 nel's wave-surface gives us (he quite unsuspected phenomenon of 

 double refraction. Why does nature make a point of honoring our 



