112 JAMES CLERK MAXWELL. [CHAP. V. 



practical knowledge of locality, extension, and figure as pro- 

 perties of bodies, and we actually perceive colour and angular 

 dimension. 



And if we take time into account (as we must always 

 do, for no sense is instantaneous), we perceive relative 

 angular motion. 



By the sense of hearing we perceive the intensity, 

 rapidity, and quality of the vibrations of the surrounding 

 medium. 



By taste and smell we perceive the effects which liquids 

 and aeriform bodies have on the nerves. 



By touch we become acquainted with many conditions 

 and qualities of bodies. 



1. The actual dimensions of solid bodies in three dimen- 

 sions, as compared with the dimensions of our own bodies. 



2. The nature of the surface ; its roughness or smooth- 

 ness. 



3. The state of the body with reference to heat. 



To this is to be referred the sensation of wetness and 

 dryness, on account of the close contact which fluids have 

 with the skin. 



By means of touch, combined with pressure and motion, 

 we perceive 



1. Hardness and softness, comprehending elasticity, 

 friability, tenacity, flexibility, rigidity, fluidity, etc. 



2. Friction, vibration, weight, motion, and the like. 

 The sensations of hunger and thirst, fatigue, and many 



others, have no relation to the properties of bodies. 



LUCRETIUS ON EMPTY SPACE. 



Nee tamen undique corporea stipata tenentur 

 Omnia natura, namque est in rebus Inane. 

 Quod tibi cognosse in multis erit utile rebus 

 Nee sinet errantem dubitare et quserere semper 

 De summa rerum ; et nostris diffidere dictis. 

 Quapropter locus est intactus Inane Vacansque 

 Quod si non esset, nulla ratione moveri 



