ON THE RELATION OF OPTICS TO PAINTING. 85 



spective drawing is however of but little avail in the 

 case of irregular shapes, rough blocks of rock and ice, 

 masses of foliage, and the like ; that this is so, is best 

 seen in photographs, where the perspective and shading 

 may be absolutely correct, and yet the total impression 

 is indistinct and confused. 



When human habitations are seen in a picture, they 

 represent to the observer the direction of the hori- 

 zontal surfaces at the place at which they stand ; and 

 in comparison therewith the inclination of the ground, 

 which without them would often be difficult to repre- 

 sent. 



The apparent magnitude which objects, whose 

 actual magnitude is known, present in different parts 

 of the picture must also be taken into account. Men 

 and animals, as well as familiar trees, are useful to the 

 painter in this respect. In the more distant centre of 

 the landscape they appear smaller than in the fore- 

 ground, and thus their apparent magnitude furnishes 

 a measure of the distance at which they are placed. 



Shadows, and more especially double ones, are of 

 great importance. You all know how much more 

 distinct is the impression which a well-shaded drawing 

 gives as distinguished from an outline ; the shading is 

 hence one of the most difficult, but at the same time 

 most effective, elements in the productions of the 

 draughtsman and painter. It is his task to imitate 



