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TWO:It is to be regretted that there have not been books especially prepared to instruct mechanical students in the relations between heat, force, motion, and practical mechanism. The subject is, of course, treated at great length in modern scientific works, but is not connected with the operations of machinery in a way to be easily understood by beginners. A treatise on the subject, called "The Correlation and Conservation of Forces," published by D. Appleton & Co. of New York, is perhaps as good a book on the subject as can at this time be referred to. The work contains papers contributed by Professors Carpenter, Grove, Helmholtz, Faraday, and others, and has the advantage of arrangement in short sections, that compass the subject without making it tedious.It is, after all, very questionable whether human happiness would be increased by suppressing the thought of death as something to be feared. George Eliot, in her Legend of Jubal, certainly expresses the contrary opinion.180 The finest edge of enjoyment would be taken off if we forgot its essentially transitory character. The free man may, in Spinoza��s words, think of nothing less than of death; but he cannot prevent the sunken shadow from throwing all his thoughts of life into higher and more luminous relief. The ideal enjoyment afforded by literature would lose much of its zest were we to discard all sympathy with the fears and sorrows on which our mortal condition has enabled it so largely to draw��the lacrimae rerum, which Lucretius himself has turned to such admirable account. And the whole treasure of happiness due to mutual affection must gain by our remembrance that the time granted for its exercise is always limited, and may at any moment be brought to an end��or rather, such an94 effect might be looked for were this remembrance more constantly present to our minds.