SEEING DOUBLE. 



self confronted with a problem which he 

 modestly admits his inability to solve : 



" To count her horns wi' a' my power 



I set mysel' : 



But whether she had three or four 

 I couldna tell." 



Let us see whether science can explain the 

 poet's difficulty. 



The diagram in Fig. 48, which represents 



L.E 



FIG. 48. THE MOON AS SEEN BY A MAN WHO IS " FOU'. 



the facts in exaggerated proportions, will help 

 the explanation. 



An ordinary observer of the moon, adjust- 

 ing his eyes so that their central lines of vision 

 meet in A at the distance of the object, and 

 at its centre, would receive in his right eye, 

 R E, an image filling the angle outlined by 

 the dash lines, and in his left eye, L E, an 

 image with its boundaries marked by the dotted 

 lines. As these images are identically related 

 to the point A, which is the centre of the field 

 of vision for both eyes, both eyes receive 

 the same image in the same part of the field 



223 



