i885.j 
Ignoramus et Ignorabimus. 467 
or deaf, or smell-less race of people, could such be found, 
that their number of senses was the maximum possible. 
But we may easily show that many additional senses are 
perfectly within the range of possibility. We all, in these 
days, hold that not merely sound, but light and heat are due 
to vibratory or undulatory motion. So be it : the vibrations 
which impress us as sound are at the rate of not more than 
20,000 per second. But the slowest of the vibrations which 
impress us as light are after the rate of 400 millions per 
second. As it has been pointed out by Prof. Pierce, of 
Cambridge (U.S.A.) between these two limits there is room 
for more than forty additional senses, each of which might 
convey to the sensorium of an animal a totally distinct "set 
of impiessions. That we are not provided with organs upon 
which such vibrations can reaCt is surely a very lame proof 
ot their impossibility. Some persons suspedt that certain 
inserts may possess one such sense, if not more than one. 
Others raise the insoluble question whether additional 
organs of sense may not be evolved in man either in coming 
generations or in a future state of existence. But such 
speculations are for the present idle. We can no more form 
any distinct idea of a number of new senses than we can of 
n dimensions in space. 
I his, however, is totally wide of our immediate purpose. 
Unless we are prepared to deny the possible existence of 
such senses we must admit that our present insight into 
Nature is most fragmentary. We are like men gazing upon 
a nocturnal landscape upon which fall five narrow beams of 
light from the windows of a castle, leaving broad regions 
between them unilluminated. What these dark spaces^may 
contain it is impossible for them to say ; but they will be 
presumptuous in the extreme if they venture to assert that 
they have a complete view of the entire region, that they 
see all which does exist, and that whatever they fail to see 
is “ impossible.” Yet this is exactly the position which men 
of great reputation have not unfrequently taken. Hence 
true men of Science, fully alive to the responsibilities of 
their position, are now very reluCtant to pronounce on 
“ impossibilities.” 
But there is no occasion for us to indulge in conjectures 
concerning the possible information which might be con- 
veyed to us by other senses if we had them. Those which 
we do possess fall very far short, each in its respective 
sphere, of giving us complete information. Let us look 
first at the most highly developed of all, our light-sense. 
Every tyro in optics knows that the retina of the human 
