^28 Transactions of the Boyal Society of South Africa. 
a state of existence deprived of the sense of sight, not only in the 
individual but throughout the human race. The phenomenon of light 
could doubtless still exist and even be capable of exerting certain physio- 
logical action ; but this phenomenon is one with which we are primarily 
cognisant through the direct physiological action on the optical nerves 
and without which the intercourse of the individual with the external 
world is perhaps limited by the further senses of "sound," "touch," 
"smell," and "taste." All these senses, even including the first, are 
brought into operation only by closely adjacent surroundings, whereas the 
additional sense of sight, apart from its use as a means of communica- 
tion between individuals, is the sole remaining sense by which we can 
obtain information regarding unexplored and otherwise inaccessible 
regions. 
I venture to doubt whether under such conditions the human intellect 
would have risen to such primary conceptions as that of a " point " and 
a "line," let alone a " straight line," and whether even the most primitive 
of the sciences, that of geometry, could have originated, though perhaps a 
sense of geometrical form might have been developed through the touch. 
Be that as it may, however, it is perhaps not too much to say that our 
knowledge of the extra-terrestrial universe has at least until recently been 
derived solely through the medium of those ethereal vibrations which we 
call light, to which our eyes respond, thus communicating with the brain ; 
and though this physical phenomenon might conceivably have existed 
apart from the existence of human or other eyes, its existence could 
scarcely have been recognised and the science of astronomy which deals 
primarily with extra-terrestrial phenomena could hardly have been. 
Thus it is that the development of this science has been largely 
concurrent with the developmient of those instruments by which the 
optical eiiiciency of the eye has been increased. 
The earliest observations were made with the unaided eye, the results 
which have come down to us being duly recorded either in the form 
•of descriptions or drawings, or even in some cases by more or less exact 
measurements. The introduction of the telescope not only immediately 
opened up fields of vision previously inaccessible, but facilitated in a very 
marked degree the precision with which measurements could be made, 
and for about three centuries the telescope has been used as a direct aid 
to the visual organ. It is improbable that this method of observation will 
ever be superseded, but there is to-day a growing tendency to replace the 
human eye at the end of the telescope by the photographic camera. 
The advantages of the method are twofold. 
(1) Objects which are too faint to be seen with the eye may yet be 
photographed by a sufficient extension of the time of exposure, and our 
power of penetrating the confines of space is thereby increased. 
