744 THE POPULAR SCIENCE MONTHLY. 



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 chair- 

 man 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 appa- 

 ratus 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 ac- 

 companied with an equivalent radiation of heat, and also that the in- 

 crease of light, and radiant heat in a flame of hydrogen, by the intro- 

 duction 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 ap- 

 plication 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, accord- 

 ing 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 expo- 

 sition 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 thunder-storm ; and an 

 essay on the principal source of the power which does the work of de- 

 veloping the plant in the bud, and the animal in the egg. 



He has also published a theory of elementary education, in his ad- 

 dress 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. 



