These various writings raise many points of interest regarding M. Comte’s personal history, and some, not without philosophic bearings, respecting his mental habits:  from all which matters we shall abstain, with the exception of two, which he himself proclaimed with great emphasis, and a knowledge of which is almost indispensable to an apprehension of the characteristic difference between his second career and his first.  It should be known that during his later life, and even before completing his first great treatise, M. Comte adopted a rule, to which he very rarely made any exception:  to abstain systematically, not only from newspapers or periodical publications, even scientific, but from all reading whatever, except a few favourite poets in the ancient and modern European languages.  This abstinence he practised for the sake of mental health; by way, as he said, of “hygiene cerebrale.”  We are far from thinking that the practice has nothing whatever to recommend it.  For most thinkers, doubtless, it would be a very unwise one; but we will not affirm that it may not sometimes be advantageous to a mind of the peculiar quality of M. Comte’s—­one that can usefully devote itself to following out to the remotest developments a particular line of meditations, of so arduous a kind that the complete concentration of the intellect upon its own thoughts is almost a necessary condition of success.  When a mind of this character has laboriously and conscientiously laid in beforehand, as M. Comte had done, an ample stock of materials, he may be justified in thinking that he will contribute most to the mental wealth of mankind by occupying himself solely in working upon these, without distracting his attention by continually taking in more matter, or keeping a communication open with other independent intellects.  The practice, therefore, may be legitimate; but no one should adopt it without being aware of what he loses by it.  He must resign the pretension of arriving at the whole truth on the subject, whatever it be, of his meditations.  That he should effect this, even on a narrow subject, by the mere force of his own mind, building on the foundations of his predecessors, without aid or correction from his contemporaries, is simply impossible.  He may do eminent service by elaborating certain sides of the truth, but he must expect to find that there are other sides which have wholly escaped his attention.  However great his powers, everything that he can do without the aid of incessant remindings from other thinkers, is merely provisional, and will require a thorough revision.  He ought to be aware of this, and accept it with his eyes open, regarding himself as a pioneer, not a constructor.  If he thinks that he can contribute most towards the elements of the final synthesis by following out his own original thoughts as far as they will go, leaving to other thinkers, or to himself at a subsequent time, the business of adjusting them to the thoughts by which they ought to be accompanied, he is right in doing so.  But he deludes himself if he imagines that any conclusions he can arrive at, while he practises M. Comte’s rule of hygiene cerebrale, can possibly be definitive.