As further proof of this statement, let me again quote from Clerk Maxwell. In the quotation already given in this Art. we have seen that the pressure of sunlight on a square foot is equal to 83.4 lb. He adds the following words to those already quoted: "A flat body exposed to sunlight would experience this pressure on its illuminated side only, and would therefore be repelled from the side on which the light falls." Now if more conclusive proof of the correctness of the argument I am advancing were required, I do not think it could be given from any greater authority than that just quoted. Coming from the pen of one of the most brilliant scientists that the past century has known, I venture to think the opinion will be received with that due weight which it demands. This statement of Clerk Maxwell's has received, however, definite and experimental proof from Professor Lebedew of Moscow University, and by Nichols and Hull of America. The former has given, in the _Annalen der Physik_ for November 1901, the results of his experiments in relation to the pressure of light. The following are the results: He proved, 1st, that the incident beam of light exerts pressure both upon an absorbing and a reflecting body; 2nd, that the pressure of light is proportionate to the amount of incident energy, and is independent of the colour of light; 3rd, that the pressure of light corresponds with the forces of radiation as calculated by Maxwell. About the same time, Nichols and Hull of America were engaged upon experiments relating to the pressure of light waves, and their results were published in the November _Physical Review_, 1901. Thus, from two separate and independent sources, Maxwell's equations as to the pressure which light waves exert upon any body on which they fall received definite experimental confirmation. The repulsive power of the light waves receives further confirmation from that theory known as the electro-magnetic theory, which supposes light to be nothing more or less than an electro-magnetic phenomenon; that is to say, it is directly or indirectly due to the action of electric currents.