MESSRS. MUNN amp; Co.mdash;It has often made me sad to see so many of our apprentice boys idle away their useful moments while out of shop. If a young man wishes to be master of his business, he must be attentive to store his mind with useful information, derived from reading, good conversation, and experiment. But our young men from eighteen to twenty one years (I admit there are some noble exceptionsmdash;I speak of the mass,) spend their spare moments in enjoying themselvesmdash;as it is called, among silly peoplemdash;or in reading trifling books, or nonsensical love stories.mdash; This age in a man's life has a potentinfluence according to the way it is improved or mis-improved, on his future welfare, his value to himself, his relatives, and country. A young man who completes his apprenticeship carrying with him a character of excellence for industry, honesty, and skill, is worth his weight in gold to himself, friends, and country. With the favor of the Scientific American, I say unto youmdash;young men of our glorious land, make up your minds, take your stand wiik a.fesBimdash;Jafarnnination. -ta spend your spare moments in useful reading, reflection, good conversation, writing, draughting, amp;c, and to work faithfully and honestly during working hours, so as to become competent, skilful, and intelligent workmen. Our manufacturers are calling loud lor master mechanics, but qualified men are not easily found. Young mechanics think of this; the innocent amusements are yours, they do good ; but do not neglect to improve the moments by wasting them in trifling pleasures. E.H., of Pa. N. B. I hereby send for five copies of the Scientific American, which 1 will present to apprentices in our coach factory, believing they will be to them of great benefit.