THE WAVE THEORY OF LIGHT. 301 



pleasure of illustrating them to you by anything 

 comparable with the splendid and instructive 

 experiments which many of you have already 

 seen. It is satisfactory to me to know that so 

 many of you, now present, are so thoroughly 

 prepared to understand anything I can say, that 

 those who have seen the experiments will not 

 feel their absence at this time. At the same time 

 I wish to make them intelligible to those who have 

 not had the advantages to be gained by a 

 systematic course of lectures. I must say, in the 

 first place, without further preface, as time is 

 short and the subject is long, simply that sound 

 and light are both due to vibrations propagated 

 in the manner of waves ; and I shall endeavour 

 in the first place to define the manner of propa- 

 gation and the mode of motion that constitute 

 those two subjects of our senses, the sense of sound 

 and the sense of light. 



Each is due to vibrations, but the vibrations 

 of light differ widely from the vibrations of sound. 

 Something that I can tell you more easily than 

 anything in the way of dynamics or mathematics 



