such wise as to give back an image turned to face its original. Or should we accept the view maintained by other philosophers that rays are emitted from our body? According to Plato these rays are filtered forth from the centre of our eyes and mingle and blend with the light of the world without us; according to Archytas they issue forth from us without any external support; according to the Stoics these rays are called into action[8] by the tension of the air: all agree that, when these emanations strike any dense, smooth, and shining surface, they return to the surface from which they proceeded in such manner that the angle of incidence is equal to the angle of reflection, and as a result that which they approach and touch without the mirror is imaged within the mirror. [Footnote 8: _facti_ MSS.] 16. What think you? Should not philosophers make all these problems subjects of research and inquiry and in solitary study look into mirrors of every kind, solid and liquid? There is also over and above these questions further matter for discussion. For instance, why is it that in flat mirrors all images and objects reflected are shown in almost precisely their original dimensions, whereas in convex and spherical mirrors everything is seen smaller, in concave mirrors on the other hand larger than nature? Why again and under what circumstances are left and right reversed? When does one and the same mirror seem now to withdraw the image into its depths, now to extrude it forth to view? Why do concave mirrors when held at right angles to the rays of the sun kindle tinder set opposite them? What is the cause of the prismatic colours of the rainbow, or of the appearance in heaven of two rival images of the sun, with sundry other phenomena treated in a monumental volume by Archimedes of Syracuse, a man who showed extraordinary and unique subtlety in all branches of geometry, but was perhaps particularly remarkable for his frequent and attentive inspection of mirrors. If you had only read this book, Aemilianus, and, instead of devoting yourself to the study of your fields and their dull clods, had studied the mathematician's slate and blackboard, believe me, although your face is hideous enough for a tragic mask of Thyestes, you would assuredly, in your desire for the acquisition of knowledge, look into the glass and sometimes leave your plough to marvel at the numberless furrows with which wrinkles have scored your face.