Does this indicate that our senses have gradually become more acute and accurate? No, no one has asserted that the sensitiveness of the organs of sense was less thousands of years ago than it is now; the sensation has not changed, but “we see in this evolution of consciousness of colour how perception goes hand in hand with the evolution of language, and how, by a very slow process, every definite concept is developed out of an infinitude of indistinct perceptions.”[56] The names of colours have not been applied arbitrarily, any more than the names given to divinities. Blue, for instance, owes its origin to the visible results of violence, or of an accident; the science of etymology shows us that the Old Norse words, blár, blá, blatt, which now mean blue, meant originally the livid colour of a bruise. Grimm traces these words back to the Gothic _bliggvan_, to strike; and he quotes as an analogous case the Latin _cæsius_--a bluish grey, from _cædere_, to cut. If the assertion that blue and green are rarely mentioned until a late date be correct, it would follow that they had been worked out of an infinity of colours before they took their place definitely as the colour of the sky and the colour of the trees and grass. As we trace etymology to its source, we see how man’s perception was confused at first. From the Sanscrit root _ghar_, which has many different meanings, such as to heat, to melt, to drip, to burn, to shine, come not only many words--heat, oven, warmth, and brightness, but also the names of many bright colours, all varying between yellow, green, red, and white. But the most striking example is afforded by the Sanscrit word _ak-tu_. Here we have the first instance of the uncertainty in the meaning of the names of colours which pervades all languages, and which can be terminated at last by scientific definition only. This word has two opposite meanings--a light tinge or ray of light, and also a dark tinge, and night; this same word in Greek, _ak-tis_, means a ray of light. Thus, whilst ideas are not definitely named, even the most simple, such as those of white and black, are not realised; philosophers have long known this, but the learned in physical science seem only recently to have drawn attention to the fact. Virchow was the first to make the following assertion: “Only after their perceptions have become fixed by language, are the senses brought to a conscious possession and a real understanding of them.”[57] Surgeons have explained that the faculty of sight proceeds from the movement of an unknown medium, which in the case of light has been called ether, this strikes the retina, and is conveyed to the brain by the optic nerve; “but what relation there is between the effect, namely, our sensation of red, and the cause, namely, the 500 millions of millions of vibrations of ether in one second, neither philosophy nor physical science has yet been able to explain.”[58]