Oc 



467 

 P7 



PREFACE 



IN the course of the last few years the author 

 has lectured on the Pressure oi Light in many 

 places. Some of the lectures have already been 

 published in full or in abstract. In this book the 

 substance of these lectures is set forth more com- 

 pletely and in greater detail than was possible in 

 any one lecture. 



For readers who desire to study the mathe- 

 matical calculations involved in the theory of the 

 subject, a series of notes is appended. 



July 1910. 



