388 NATURE AND MAN. 



is simply a general expression of one of the conditions under 

 which that force is exerted ; and the embodiment of our know- 

 ledge of those conditions into such general expressions, enables 

 me to predict other phenomena at first sight having no relation 

 to them. Thus we have the scientific certainty that the magnetic 

 bar, when moved within a coil of copper wire, will generate in 

 that wire an electric current, which, when conducted to any 

 distance, and made to pass in a coil of wire around a soft iron 

 bar, shall render it capable of attracting iron, deflecting the 

 compass-needle, and so on. Thus, to say that a piece of iron 

 has magnetic properties, is only another way of saying that it is 

 a magnet ; but whilst the ancients only knew of a magnet as 

 having the power of attracting iron, we know that it is capable 

 of doing many other things ; and of this capacity, the phrase 

 " magnetic properties " is nothing more than a convenient expres- 

 sion, embodying the general fact that the piece of iron which is 

 shown to be possessed of any one of them, possesses all the rest. 



I might follow the same train of reasoning into every depart- 

 ment of scientific inquiry, and show that what has been called the 

 " promise and potency " of matter is nothing else than a phrase 

 embodying a general conception of the various uniformities 

 observable in its actions, and not helping us in the least degree 

 to an explanation of those uniformities. But as the real signifi- 

 cance — or, rather, z^^significance — of the term "property" be- 

 comes most apparent when it is used to designate the respective 

 potentialities of difi"erent species of organic germs, I shall defer 

 until the latter part of my address what I would further say upon 

 this point. 



One of the most remarkable among the many doctrines which 

 have been recently propounded to account for particular groups 

 of physical phenomena, is that known as the kinetic theory of 

 gases ; to which the eminent ability of the late Professor Clark 

 Maxwell gave such a remarkable development, that, according to 

 the statement of one of its ablest expositors (Professor Tait), it 

 is "capable of explaining almost everything that we know with 

 "reference to the behaviour of gases, and, perhaps, even of 

 "vapours." The application of high mathematical reasoning to 

 the facts of observation seems not only to justify, but to necessi- 



