Horace Mann quotes

Congressional speech (1849)
Context: I affirm, in words as true and literal as any that belong to geometry, that the man who withholds knowledge from a child not only works diabolical miracles for the destruction of good, but for the creation of evil also. He who shuts out truth, by the same act opens the door to all the error that supplies its place. Ignorance breeds monsters to fill up all the vacuities of the soul that are unoccupied by the verities of knowledge. He who dethrones the idea of law, bids chaos welcome in its stead. Superstition is the mathematical complement of religious truth; and just so much less as the life of a human being is reclaimed to good, just so much more is it delivered over to evil. The man or the institution, therefore, that withholds knowledge from a child, or from a race of children, exercises the awful power of changing the world in which they are to live, just as much as though he should annihilate all that is most lovely and grand in this planet of ours, or transport the victim of his cruelty to some dark and frigid zone of the universe, where the sweets of knowledge are unknown, and the terrors of ignorance hold their undisputed and remorseless reign.

"Printing and Paper Making" in The Common School Journal Vol. V, No. 3 (1 February 1843)
Context: Every school boy and school girl who has arrived at the age of reflection ought to know something about the history of the art of printing, papermaking, and so forth. … All children will work better if pleased with their tools; and there are no tools more ingeniously wrought, or more potent than those which belong to the art of the printer. Dynasties and governments used to be attacked and defended by arms; now the attack and the defence are mainly carried on by types. To sustain any scheme of state policy, to uphold one administration or to demolish another, types, not soldiers, are brought into line. Hostile parties, and sometimes hostile nations, instead of fitting out martial or naval expeditions, establish printing presses, and discharge pamphlets or octavoes at each other, instead of cannon balls. The poniard and the stiletto were once the resource of a murderous spirit; now the vengeance, which formerly would assassinate in the dark, libels character, in the light of day, through the medium of the press.
But through this instrumentality good can be wrought as well as evil. Knowledge can be acquired, diffused, perpetuated. An invisible, inaudible, intangible thought in the silent chambers of the mind, breaks away from its confinement, becomes imbodied in a sign, is multiplied by myriads, traverses the earth, and goes resounding down to the latest posterity.

Quoted in Thoughts (1901) by Jessie K. Freeman and Sarah S. B. Yule, p. 83, and in Collect Writings of Russell H. Conwell (1925), Vol. 1, p. 396
Context: Doing nothing for others is the undoing of ourselves. We must purposely be kind and generous, or we miss the best part of existence. The heart which goes out of itself gets large and full. This is the great secret of the inner life. We do ourselves the most good doing something for others.

A Few Thoughts for a Young Man (1850)
Context: The laws of nature are sublime, but there is a moral sublimity before which the highest intelligences must kneel and adore. The laws by which the winds blow, and the tides of the ocean, like a vast clepsydra, measure, with inimitable exactness, the hours of ever-flowing time; the laws by which the planets roll, and the sun vivifies and paints; the laws which preside over the subtle combinations of chemistry, and the amazing velocities of electricity; the laws of germination and production in the vegetable and animal worlds, — all these, radiant with eternal beauty as they are, and exalted above all the objects of sense, still wane and pale before the Moral Glories that apparel the universe in their celestial light. The heart can put on charms which no beauty of known things, nor imagination of the unknown, can aspire to emulate. Virtue shines in native colors, purer and brighter than pearl, or diamond, or prism, can reflect. Arabian gardens in their bloom can exhale no such sweetness as charity diffuses. Beneficence is godlike, and he who does most good to his fellow-man is the Master of Masters, and has learned the Art of Arts. Enrich and embellish the universe as you will, it is only a fit temple for the heart that loves truth with a supreme love. Inanimate vastness excites wonder; knowledge kindles admiration, but love enraptures the soul. Scientific truth is marvellous, but moral truth is divine; and whoever breathes its air and walks by its light, has found the lost paradise. For him, a new heaven and a new earth have already been created. His home is the sanctuary of God, the Holy of Holies. <!-- p. 35

As quoted in A Dictionary of Thoughts : Being a Cyclopedia of Laconic Quotations from the Best Authors of the World, both Ancient and Modern (1908) edited by Tryon Edwards

Philip James Bailey, in Festus (1839), misattribution of this to Mann seems to have only started in recent years, on the internet.
Misattributed

Lecture 7
Lectures on Education (1855)

Sir Thomas Browne, as quoted by The Pleasures of Life (1891), by John Lubbock, p. 11
Misattributed