

Dr Kuhl on the Vegetable Productions of' Madeira. 119 



balance of two circumstances combined in the same represen- 

 tation, viz. 1. The general position of the face presented to 

 the spectator ; and, 2. The turn of the eyes from that position. 



In the same manner as the general position of the face car- 

 ries the eyes along with it, so a change in the position of the 

 eyes carries the face along with them. This fact, which is 

 not mentioned by Dr Wollaston, is not less surprising than its 

 counterpart, and may be well illustrated by causing a pair of 

 moveable eyes to oscillate in the sockets of the eyes of a picture. 



Dr Wollaston next proceeds to explain a fact which every 

 person must have observed, that, if the eyes of a portrait look at 

 the spectator when he stands in front of the picture, they fol- 

 low and appear to look at him in every other direction. His 

 explanation and illustration of this is every way satisfactory ; 

 but not so popular as we think it may be made. The follow- 

 ing illustration appears to us more easily comprehended. If 

 a picture represents three soldiers, each firing a musket in 

 parallel directions, and if the musket of the middle one is 

 pointed accurately to one eye of the spectator, the other being 

 supposed shut, then the muzzle of the musket will be exactly 

 circular, and the spectator will see down the barrel, and no part 

 of the right or left side of the barrel. In like manner, the specta- 

 tor will see the left side of the barrel of the musket opposite his 

 left hand, and the right side of the barrel of the musket oppo- 

 site his right hand. If the spectator now changes his place, and 

 takes ever such an oblique position, either laterally or vertically, 

 he must see the same thing, because nothing else is painted on 

 the canvas. The gun of the middle soldier must always point 

 to the eye of the spectator, the gun of the other to the right 

 of him, and the gun of the third to the left of him. They 

 will, therefore, all three seem to move as he moves, and fol- 

 low him in his motions. The same reasoning is applicable to 

 perspective buildings. 



Art. XXIII. — On the Vegetable Productions of the Island 

 of Madeira. By Dr H. Kuhl. 



The following account of the vegetation of the island of Ma- 

 deira is given in the " Botcmische Zeitomgy as the substance 



