Scientific Lectures. 263 



is ]ilaecd in a. I'ooiu, M'itli wliicl! lie is ])nrtial]y familiar, in Avliicli no 

 light enters, and how instantly (h»es the mind conceive the idea of 

 space, and strive to constrnct things under it. lie tries first to 

 establish his ])resent position, and then, by feeling along, to establish 

 the relation between the iirst objeets he meets, and so to construct 

 tlieni as to get an idea of their whereabouts. Passing from one por- 

 tion of the room to another, he avoids this ol)ject and reaches that, 

 conjectuj-ally locating each according to his general conception. Thus 

 one who has lost his rights takes u}) anew, in connection with trials, 

 tlie external world, and linally acquires a skill which is astonishing and 

 startling to the rest of us, who have not been accustomed to interpret 

 these things in the form in which he interprets them. AVitli the idea 

 of time the geologist constructs the past physical history of the globe. 

 He assigns long periods to the formation of strata, according to their 

 thickness and material, and passes from one formation to another with 

 vaiwing intervals. His entire science arises under the motion of time, 

 the time adequate to explain cei'tain effects. The spectrescope dis- 

 closes to us the nature of the sun, because of tlie idea of causation 

 with which we inter^jret its luminous and dark lines. In the ideas, 

 therefore, M-hicli the mind furnishes, we find the grounds and direc- 

 tions of knowledge. Some of these we indicate as affording the basis 

 of a division between physical and mental science. 



Existence. 

 ]Sruml)er. 

 Eesemblance. 

 Space, ) riT \ Consciousness, 



Cause and Effect. ( "®' i S})ontaneity. 



The first three of these apply equally to all things. We may be 

 aware, through the senses, of an object l)efore us, as this desk ; but it 

 is not till the mind su])plies the idea of existence that ^\'e think 

 directly concei-ning it. It is the sense (^f reidity, of valid l)eing, 

 springs from the mind itself, not from the sensations as a sensation. 

 The same is true of number. As a whole my hand is one ; consid- 

 ered in reference to its fingers it presents four; in reference to their 

 joints, twelve. In whatevei- way I look at it. a new numerical 

 expi-ession bel<_>ngs to it. Of molecules, it contains an iiidelinite 

 number. Of sim[)le elements, or of homogeneous substances, a 

 restricted nund)er. Its lengtli and breath and thickness vary in 

 expression with the unit ol'nu'a-in-ement used by me; and thus 1 am 



