5 6 THE POPULAR SCIENCE MONTHLY. 



Declining to attempt solutions of the origin and destiny of the uni- 

 verse, we would endeavor to attack undone work for mankind near at 

 hand, neglecting in the mean time all discussion of the remote and im- 

 possible. 



Not only in their overrating the powers of the intellect did our 

 forefathers err, but also as seriously in their views of knowable truth 

 did they exhibit immaturity of thought. Truth may be defined as the 

 reality of things underlying our partial knowledge of them. Except 

 in the limited area of axiom, our knowledge is imperfect and incom- 

 plete. On examination, it proves to consist largely of mere signs and 

 symbols. We can state the law whereby gravitation acts, but the force 

 itself eludes our scrutiny. We can formulate its rate and measure its 

 quantity, but why bodies tend toward each other throughout universal 

 Nature is as little known to our acutest physicists as to the least in- 

 formed savages. All analogy requires us to think that a medium is 

 necessary for the conveyance of the attraction, yet, if there be a me- 

 dium, how does it do its work, and that too across the diameter of the 

 visible universe with practical instantaneity ? So too with the proper- 

 ties of substances which are surely among the simplest things we can 

 consider. What is the essential difference between iron and lead, and 

 why does water always freeze in six-petaled crystals ? Such questions, 

 which lie at the very threshold of the temple of inquiry, show us how 

 hard is our task of getting below our labels, our names of things, and 

 pursuing investigation more than a single remove from appearance. 



At the risk of being tedious, I shall take an example of the growth 

 of our information about a single substance, to illustrate the indefi- 

 nitely great extensions of knowledge which are possible to us, in every 

 direction in which we may seek it this in contrast with the views 

 of knowable truth which were current in the infancy of information. 

 Iron had, doubtless, in very remote times, been observed to be tena- 

 cious and malleable ; of value, therefore, in making of tools and 

 weapons. Later on its magnetism was noticed, and, at some uncertain 

 date, in China probably, it began to be used in navigation as the mari- 

 ner's compass. The rusting of the metal must have been observed 

 very long ago ; yet it is little more than a century since that com- 

 mon fact was rationally explained, and since the chemical relations of 

 iron began to be studied. Examination has determined its crystalline 

 structure ; its capacity as a transmitter of sound, heat, and electricity ; 

 and its improved tenacity, when united with carbon, to form steel. 

 The long catalogue of its various properties does not seem to be ap- 

 proaching a limit, but rather the reverse. Within recent years spec- 

 trum analysis has determined the peculiar lines, several hundred in 

 number, which enable it to be identified as a fiery vapor, alike in the 

 flame of the laboratory or in the remote orbs of space. The telephone 

 proves that a small disk of the metal conceals within its structure the 

 subtile means of converting sound-waves into electrical tremors, and 



