4 THE PRESIDENTIAL ADDRESS 



so far as it is understood. I shall show how the compromise and 

 balance between different competing considerations which is seen 

 in its design can be artificially modified for special purposes. All 

 engineering designs are a matter of compromise. You cannot 

 have everything. The unassisted eye has a field of view extending 

 nearly over a hemisphere. It gives an indication very quickly 

 and allows comparatively rapid changes to be followed. It responds 

 best to the wave-lengths actually most abundant in daylight or 

 moonlight. This combination of qualities is ideal for what we 

 believe to be nature's primary purpose, that is for finding subsistence 

 under primitive conditions and for fighting the battle of life against 

 natural enemies. But by sacrificing some of these qualities, and in 

 particular the large field of view, we can enhance others for purposes 

 of research. We may modify the lens system by artificial additions 

 over a wide range for examining the very distant or the very small. 

 We can supplement and enormously enhance the power of colour 

 discrimination which nature has given us. By abandoning the use 

 of the retina and substituting the photographic plate as an artificial 

 retina, we can increase very largely the range of spectrum which can 

 be utilised. This last extension has its special possibilities, par- 

 ticularly in the direction of using waves smaller than ordinary, even 

 down to those which are associated with a moving electron. By 

 using the photoelectric cell as another substitute for the retina with 

 electric wire instead of optic nerve and a recording galvanometer 

 instead of the brain we can make the impressions metrical and can 

 record them on paper. We can count photons and other particulate 

 forms of energy as well. We can explore the structure of atoms, 

 examine the disintegration of radioactive bodies, and trace out the 

 mutual relation of the elements. Indeed, by elaborating this train 

 of thought a little further almost the whole range of observational 

 science could be covered. But within the compass of an hour or 

 so one must not be too ambitious. It is not my purpose to stray very 

 far from what might, by a slight stretch of language, fall under the 

 heading of extending the powers of the eye. 



Most people who have a smattering of science now know the 

 comparison of the eye with the camera obscura, or better, with the 

 modern photographic camera — with its lens, iris, diaphragm, 

 focussing adjustment and ground glass screen, the latter correspond- 

 ing to the retina. The comparison does not go very far, for it does 

 not enter upon how the message is conveyed to the brain and appre- 

 hended by the mind ; or even upon the minor mystery of how colours 

 are discriminated. Nevertheless, it would be a great mistake to 

 suppose that the knowledge which is embodied in this comparison 

 was easily arrived at. For example, many acute minds in antiquity 

 thought that light originated in the eye rather than in the object 



