POLARISED L 



BY W. SPOTTISWOODE, F.E.S. 



ACCORDING to the proposal of the director who has organised 

 the present course, the lecture of this morning will be devoted 

 to a description of some of the principal instruments used 

 for investigating polarised light, and to an explanation of 

 their use. With this purpose in view I have selected a few 

 from the magnificent collection now in the Loan Exhibition. 

 These you may now see on the table, and although they are 

 only a few out of many, I doubt not that we have enough, 

 or even more than enough, to occupy our attention during the 

 hour at our disposal. With one exception my selection has 

 been confined to the smaller and simpler instruments, partly 

 because, following the example of Professor Stokes, it will 

 be my object to explain principles rather than to repeat 

 experiments, and to indicate what may be done with instru- 

 ments of the simplest form, and even of home construction ; 

 and partly because it has been suggested that at one of the 

 evening lectures I should make use of the larger and more 

 elaborate instruments, and by their aid exhibit the magnificent 

 phenomena to which the subject gives rise. And let me here 

 take the opportunity of drawing your attention to the fact 

 that at present the collection of apparatus appertaining to 

 polarised light is unique, and that it furnishes the means of 

 exhibiting the effects in question on a scale never before 

 attempted. 



Light is said to be polarised when it exhibits certain pecu- 

 liarities, to be hereafter described, which it is not found 



VOL. II. & B 



