interruption or intermission, and without any signs of _diminution_ or _exhaustion_. In reasoning on this subject, we must not forget that _most remarkable circumstance_, that the source of the heat generated by friction in these experiments appeared to be _inexhaustible_. It is hardly necessary to add, that anything which any insulated body or system of bodies can continue to furnish _without limitation_ cannot possibly be _a material substance_; and it appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of anything capable of being excited and communicated in these experiments, except it be MOTION." In style, Professor Tyndall's work is remarkably clear, spirited, and vigorous, and many of its pages are eloquent with the beautiful enthusiasm and poetic spirit of its author. These attractions, combined with the comprehensiveness and unity of the discussion, the range and authenticity of the facts, and the delicacy, originality, and vividness of the experiments, render the work at once popular and profound. It is s classic upon the subject of which it treats. _My Days and Nights on the Battle-Field_. A Book for Boys. By "CARLETON." Boston: Ticknor and Fields. The literature of the war has already reached the dimensions of a respectable library. The public mind at the instant of the outbreak felt an assurance that it was to be one of the memorable epochs of mankind. However blinded to the significance of the previous conflicts in the forum and at the ballot-box, there was a sudden and universal instinct that their armed culmination was a world-era. The event instantly assumed its true grandeur. The previous discussions seemed local and limited. They were squabbles, we fancied, among ourselves, which did not touch the vitals of our system, and in which the world without had neither lot nor interest. Even when the fires of debate and division waxed hotter and hotter, and began to break out in violent eruptions in Congress, Kansas, throughout the South, and especially at Harper's Ferry, we still said, These are political conflicts, mob-violences, raids, abnormal eccentricities, which will pass quietly away, when the dynasty is changed, and the reins of power are fairly grasped by the successful rival. Europe sends her doctors to witness our dissolution. They go South and see the mustering of arms and the intensity of purpose, and coming North find the whole community at their usual pursuits and pleasures, regarding the controversy as a mere political breeze, and the results in which it is beginning to issue as but the waves that ever for a short season roll fiercely after the storm.