I spoke just now of comprehensive words, which should singly say what hitherto it had taken many words to say, in which a higher term has been reached than before had been attained. The value of these is incalculable. By the cutting short of lengthy explanations and tedious circuits of language, they facilitate mental processes, such as would often have been nearly or quite impossible without them; and such as have invented or put these into circulation, are benefactors of a high order to knowledge. In the ordinary traffic of life, unless our dealings are on the smallest scale, we willingly have about us our money in the shape rather of silver than of copper; and if our transactions are at all extensive, rather in gold than in silver: while, if we were setting forth upon a long and costly journey, we should be best pleased to turn even our gold coin itself into bills of exchange or circular notes; in fact, into the highest denomination of money which it was capable of assuming. How many words with which we are now perfectly familiar are for us what the circular note or bill of exchange is for the traveller or the merchant. As innumerable pence, a multitude of shillings, not a few pounds are gathered up and represented by one of these, so have we in some single word the quintessence and final result of an infinite number of anterior mental processes, ascending one above the other, until all have been at length summed up for us in that single word. This last may be compared to nothing so fitly as to some mighty river, which does not bring its flood of waters to the sea, till many rills have been swallowed up in brooks, and brooks in streams, and streams in tributary rivers, each of these affluents having lost its separate name and existence in that which at last represents and contains them all.
Science is an immense gainer by words which thus say singly, what whole sentences might with difficulty have succeeded in saying. Thus 'isothermal' is quite a modern invention; but how much is summed up by the word; what a long story is saved, as often as we speak of 'isothermal' lines. Physiologists have given the name of 'atavism' to the emerging again of a face in a family after its disappearance during two or three generations. What would have else needed a sentence is here accomplished by a word. Lord Bacon somewhere describes a certain candidate for the Chair of St. Peter as being 'papable.' There met, that is, in him all the conditions, and they were many, which would admit the choice of the Conclave falling upon him. When Bacon wrote, one to be 'papable' must have been born in lawful wedlock; must have no children nor grandchildren living; must not have a kinsman already in the Conclave; must be already a Cardinal; all which facts this single word sums up. When Aristotle, in the opening sentences of his _Rhetoric_, declares that rhetoric and logic are antistrophic,' what a wonderful insight into both, and above all into their relations to one another, does the word impart to those who have any such special training as enables them to take in all which hereby he intends. Or take a word so familiar as 'circle,' and imagine how it would fare with us, if, as often as in some long and difficult mathematical problem we needed to refer to this figure, we were obliged to introduce its entire definition, no single word representing it; and not this only, but the definition of each term employed in the definition;--how well nigh impossible it would prove to carry the whole process in the mind, or to take oversight of all its steps. Imagine a few more words struck out of the vocabulary of the mathematician, and if all activity and advance in his proper domain was not altogether arrested, yet would it be as effectually restrained and hampered as commercial intercourse would be, if in all its transactions iron or copper were the sole medium of exchange. Wherever any science is progressive, there will be progress in its nomenclature as well. Words will keep pace with things, and with more or less felicity resuming in themselves the labours of the past, will at once assist and abridge the labours of the future; like tools which, themselves the result of the finest mechanical skill, do at the same time render other and further triumphs of art possible, oftentimes such as would prove quite unattainable without them. [Footnote: See Mill, _System of Logic_, iv. 6, 3.]