ever lures her lovers to the chase, and the record of their hopes and conquests is contained in the lover’s language, made up wholly of parable and figure of speech.  There is nothing under the sun nor beyond it that does not concern man, and it is the unceasing effort of humanity, whether by letters or by science, to bring “the commerce of the mind and of things” to terms of nearer correspondence.  But Literature, ambitious to touch life on all its sides, distrusts the way of abstraction, and can hardly be brought to abandon the point of view whence things are seen in their immediate relation to the individual soul.  This kind of research is the work of letters; here are facts of human life to be noted that are never like to be numerically tabulated, changes and developments that defy all metrical standards to be traced and described.  The greater men of science have been cast in so generous a mould that they have recognised the partial nature of their task; they have known how to play with science as a pastime, and to win and wear her decorations for a holiday favour.  They have not emaciated the fulness of their faculties in the name of certainty, nor cramped their humanity for the promise of a future good.  They have been the servants of Nature, not the slaves of method.  But the grammarian of the laboratory is often the victim of his trade.  He staggers forth from his workshop, where prolonged concentration on a mechanical task, directed to a provisional and doubtful goal, has dimmed his faculties; the glaring motley of the world, bathed in sunlight, dazzles him; the questions, moral, political, and personal, that his method has relegated to some future of larger knowledge, crowd upon him, clamorous for solution, not to be denied, insisting on a settlement to-day.  He is forced to make a choice, and may either forsake the divinity he serves, falling back, for the practical and aesthetic conduct of life, on those common instincts of sensuality which oscillate between the conventicle and the tavern as the poles of duty and pleasure, or, more pathetically still, he may attempt to bring the code of the observatory to bear immediately on the vagaries of the untameable world, and suffer the pedant’s disaster.  A martyr to the good that is to be, he has voluntarily maimed himself “for the kingdom of Heaven’s sake”—­if, perchance, the kingdom of Heaven might come by observation.  The enthusiasm of his self-denial shows itself in his unavailing struggle to chain language also to the bare rock of ascertained fact.  Metaphor, the poet’s right-hand weapon, he despises; all that is tentative, individual, struck off at the urging of a mood, he disclaims and suspects.  Yet the very rewards that science promises have their parallel in the domain of letters.  The discovery of likeness in the midst of difference, and of difference in the midst of likeness, is the keenest pleasure of the intellect; and literary expression, as has been said, is one long series of such discoveries, each with its thrill of incommunicable happiness, all unprecedented, and perhaps unverifiable by later experiment.  The finest instrument of these discoveries is metaphor, the spectroscope of letters.