13. Original experiments on, and exposition of, the principles of acoustics, as applied to churches and other public buildings.
14. Experiments on various instruments to be used as fog-signals.
15. A series of experiments on various illuminating materials for light-house use, and the introduction of lard-oil for lighting the coasts of the United States. This and the preceding in his office of chairman of the Committee on Experiments of the Light-House Board.
16. Experiments on heat, in which the radiation from clouds and animals in distant fields was indicated by the thermo-electrical apparatus applied to a reflecting telescope.
17. Observations on the comparative temperature of the sun-spots, and also of different portions of the sun's disk. In these experiments he was assisted by Prof. Alexander.
18. Proof that the radiant heat from a feebly luminous flame is also feeble, and that the increase of radiant light, by the introduction of a solid substance into the flame of the compound blow-pipe, is accompanied with an equivalent radiation of heat, and also that the increase of light, and radiant heat in a flame of hydrogen, by the introduction of a solid substance, is attended with a diminution in the heating power of the flame itself.
19. The reflection of heat from concave mirrors of ice, and its application to the source of the heat derived from the moon.
20. Observations, in connection with Prof. Alexander, on the red flames on the border of the sun, as observed in the annular eclipse of 1838.
21. Experiments on the phosphorogenic ray of the sun, from which it is shown that this emanation is polarizable and refrangible, according to the same laws which govern light.
22. On the penetration of the more fusible metals into those less readily melted, while in a solid state.
Besides these experimental additions to physical science, Prof. Henry is the author of twenty-five (1846-'71) reports, giving an exposition of the annual operations of the Smithsonian Institution. He has also published a series of essays on meteorology in the Patent-Office Reports, which, besides an exposition of established principles, contain many new suggestions; and, among others, the origin of the development of electricity, as exhibited in the thunderstorm; and an essay on the principal source of the power which does the work of developing the plant in the bud, and the animal in the egg.
He has also published a theory of elementary education, in his address as President of the American Association for the Advancement of Education, the principle of which is, that in instruction the order of Nature should be followed; that we should begin with the concrete and end with the abstract, the one gradually shading into the other; also the importance of early impressions, and the tendency in old age to relapse into the vices of early youth.