“An isolated person requires correspondence as a means of seeing his ideas as others see them, and thus guarding against the dogmatisms and extravagances of solitary and uncorrected speculation. No man can learn to reason and appraise from a mere perusal of the writing of others. If he live not in the world, where he can observe the public at first hand and be directed toward solid reality by the force of conversation and spoken debate, then he must sharpen his discrimination and regulate his perceptive balance by an equivalent exchange of ideas in epistolary form.”