by the Elector of Bavaria.  He went to Europe in the time of the American Revolution, and, devoting himself to scientific investigations, became the founder of the Royal Institution of Great Britain.  Davy was his associate, and, so far as the new views of heat are concerned, his disciple.  He exploded the notion of caloric, demonstrated experimentally the conversion of mechanical force into heat, and arrived at quantitative results, which, considering the roughness of his experiments, are remarkably near the established facts.  He revolved a brass cannon against a steel borer by horse-power for two and one-half hours, thereby generating heat enough to raise eighteen and three-fourths pounds of water from sixty to two hundred and twelve degrees.  Concerning the nature of heat he wrote as follows, the Italics being his own:—­“What is heat?  Is there any such thing as an igneous fluid?  Is there anything that with propriety can be called caloric?  We have seen that a very considerable quantity of heat may be excited by the friction of two metallic surfaces, and given off in a constant stream, or flux, in all directions, without 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.