The advantages which ensue from this mode of "ranging round each topic" are well described by the late Sir B. Brodie (Psychological Inquiries, 1st series, p. 18). "Our minds are so constructed that we can keep the attention fixed on a particular object until we have, as it were, looked all around it; and the mind that possesses this faculty in the greatest degree of perfection will take cognisance of relations of which another mind has no perception. It is this, much more than any difference in the abstract power of reasoning, which constitutes the vast difference which exists between the minds of different individuals; which distinguishes the far-sighted statesman from the shallow politician; the sagacious and accomplished general from the mere disciplinarian. Such also is the history, not only of the poetic genius, but also of the genius of discovery in science. 'I keep the subject,' said Sir Isaac Newton, 'constantly before me, and wait until the first dawnings open by little and little into a full light.' It was thus that, after long meditation, he was led to the invention of fluxions, and to the anticipation of the modern discovery of the combustibility of the diamond. It was thus that Harvey discovered the circulation of the blood; and that those views were suggested to Davy, which are propounded in the Bakerian lecture of 1806, and which laid the foundation of that grand series of experimental researches which terminated in the decomposition of the earths and alkalies." Dr. Tyndall also considers the case of Newton ("Fragments of Science," p. 60). "Newton pondered all these things. He had a great power of pondering. He could look into the darkest subject until it became entirely luminous. How this light arises we cannot explain; but, as a matter of fact, it does arise." Dr. Tyndall had before remarked on the question thus suggested, that "There is much in this process of pondering and its results which it is impossible to analyse. It is by a kind of inspiration that we rise from the wise and sedulous contemplation of facts to the principles on which they depend. The mind is, as it were, a photographic plate, which is gradually cleansed by the effort to think rightly, and which when so cleansed, and not before, receives impressions from the light of truth. This passage from facts to principles is called induction, which in its highest form is inspiration; but, to make it sure, the inward sight must be shown to be in accordance with outward fact. To prove or disprove the induction, we must resort to deduction and experiment."--Ibid, p. 57-8. This last remark concerns the process of verification which the accomplished writer discusses through several subsequent pages.