The subject selected by the Examiners for the Adams Prize for 1899 was<br><br>The Theory of the Aberration of Light.<br><br>The phenomena of aberration depend upon the relations of the ether and matter and must therefore be intimately associated with many other facts of nature. In the following essay an attempt is made to construct a theory of the electromagnetic field which shall be consistent with the modern interpretation of chemical, optical and magnetic phenomena in terms of electrically charged particles. That a particular case of such a theory would explain aberration was proved by H. A. Lorentz in the year 1892.<br><br>Since the essay was returned by the examiners I have thought it advisable to remove some defects and obscurities which did not appreciably affect the main argument.