16 PHYSICAL EXPRESSION. 



lastly, if the child be very cross and sulky, the sight 

 of the toy may cause no expression of joy. If, on 

 the contrary, the child be " in a very laughing 

 humour," the expression by similar stimulation 

 will be excessive in degree. 



These considerations show that the condition of 

 the subject is in part indicated in expression 

 when the subject is acted on by external forces 

 afferent to it. In speaking of reflective action 

 as a mode of expression, it will be seen that the 

 line of argument founded upon such an obser- 

 vation may be inverted. If the subject is known 

 to be constant and unchangeable in its proper- 

 ties under the same conditions, any variation in 

 the outcome of its properties or functions is due 

 to a change in the afferent forces or the environ- 

 ment. In looking at a man of known stable con- 

 stitution, in whom no disease or special defect of 

 any organ is discoverable, if we observe some 

 sudden change in the aspect of his face indicating, 

 according to our experience, grave mental anxiety, 

 we may conclude that something has happened to 

 him causing anxiety some news of disaster or 

 cause of fear, etc. The aspect of his face is the 

 expression, firstly, of his condition ; secondly, it 

 affords evidence that some event has happened 

 affecting him with fear. 



A thermometer is an instrument not changing 

 itself ; any variation in the volume of mercury in 

 the bulb and stem is due to heat : here any 

 increase in the bulk of the mercury is due to heat 

 coming to the instrument, and the rise of mercury 



