THE STREAM OF THOUGHT. 285 



a world full of contrasts, of sharp accents, of abrupt changes, 

 of picturesque light and shade. 



If the sensations we receive from a given organ have 

 their causes thus picked out for us by the conformation of 

 the organ's termination, Attention, on the other hand, out 

 of all the sensations yielded, picks out certain ones as 

 worthy of its notice and suppresses all the rest. Helm- 

 holtz's work on Optics is little more than a study of those 

 visual sensations of which common men never become 

 aware — blind spots, muscce volitantes, after-images, irradia- 

 tion, chromatic fringes, marginal changes of color, double 

 images, astigmatism, movements of accommodation and 

 convergence, retinal rivalry, and more besides. We do not 

 even know without special training on which of our eyes an 

 image falls. So habituall}' ignorant are most men of this 

 that one may be blind for years of a single eye and never 

 know the fact. 



Helmholtz says that we notice only those sensations 

 which are signs to us of things. But what are things ? Noth- 

 ing, as we shall abundantly see, but special groups of sen- 

 sible qualities, which happen practically or gestheticalh^ to 

 interest us, to which we therefore give substantive names, and 

 which we exalt to this exclusive status of independence and 

 dignity. But in itself, apart from my interest, a particular 

 dust-wreath on a windy day is just as much of an individual 

 thing, and just as much or as little deserves an individual 

 name, as my own body does. 



And then, among the sensations we get from each sepa- 

 rate thing, what happens ? The mind selects again. It 

 chooses certain of the sensations to represent the thing 

 most truly, and considers the rest as its appearances, modi- 

 fied by the conditions of the moment. Thus my table-top 

 is named square, after but one of an infinite number of 

 retinal sensations which it yields, the rest of them being 

 sensations of two acute and two obtuse angles ; but I call 

 the latter perspective views, and the four right angles the 

 true form of the table, and erect the attribute squareness 

 into the table's essence, for aesthetic reasons of my own. 

 In like manner, the real form of the circle is deemed to be 

 the sensation it gives when the line of vision is perpendicu- 



