GATEWAYS OF KNOWLEDGE.

Western Star, Issue 810, 19 January 1884, Page 6 (Supplement)

GATEWAYS OF KNOWLEDGE.

The common enumeration of the gateways of knowledge is five —taste, smell, hearing, eight, and touch, and the Irishman made out another, commonseuse—and speaking as an Irishman, he felt convinced that if that were more common to his countrymen it would do more to alleviate the woes of Ireland than anything else. What he wanted to show, however, was that there were six gateways of knowledge by the division of the sense of touch. One hundred years ago Dr Thomas Brown, professor of philosophy in the university of Glasgow, propounded this theory, making the division of roughness and resistance. The senses, he wished to explain, were heat and force, the subdivision of touch, addition to sight, hearing, taste, and smell. He did not in that favour the superstition of magnetism or mesmerism, of which they had heard so much. Clairvoyance and so on were the result of observations somewhat mixed up with wilful imposture acting on trusting minds, but if there were not a magnetic sense he wondered greatly. With a powerful dynamo-electric machine a piece of copper or silver let fall between the poles of a magnet would sink between them as through mud, slowly; and yet with a large magnet, between the poles of which a human head could be placed, there was no perceivable effect on the head. Yet he thought it possible there might be a magnetic sense, and perhaps an electric sense. There is also a distinction between the sense of hearing and the perception of sound. In the former case there is distinct and sudden pressure on the tympanum, that was yet moderate enough not to disturb the substance of the tympanum, but there was another sensation perceptible to the ear, and that was pressure above, which was perceived in a sudden change of the barometer, or the variation of air pressure, such as is experienced on going up a mountain and the going down in a diving-bell. There was a smaller division of perception which the ear is capable of, the distinction between noise and musical sound. Music is produced by regular and periodic changes of pressure and alternative augmentation and diminution of pressure. It is marvellous that in contemplating all the various differences of pressure, of laceration of the air produced by an orchestra, that all are blended into the varying of one variable pressure, and can be expressed mathematically by a varying curve, as the state aud variation of the cotton market are shown by a curved line. Eight, like hearing, is due to vibration in the air, the different colours being perceived by the eye as the nerves of the retina are excited to vibration by

different circumstances. All light rays have heating perceptions in them. The two sensations need not be separated. People might say that they could not see a black heated body in the dark, but there are qualities of radiant heat which are perceptible by the eye, and yet might contain light rays. The eye may not perceive the rays because they vibrate too slowly ; and, in fact, it is the sense of sight as well as that of hearing. The intensity of the perception depends entirely on the rapidity or otherwise of the vibration of the rays. With the senses of taste and smelling the circumstances are vastly different. They are chemical senses. There is a noticular continuity here quite different from the sense of roughness or force to be dealt with. Smell and taste might be regarded as the extremes of one sense, and they differ from the other senses inasmuch as they can be compared. The roughness of a stone cannot be compared with the shape of that stone, but the taste of a piece of cinnamon can be compared and likened to the smell of cinnamon. He had often been attacked fop enunciating this extra sense of force which applied to the others, but he could never understand the ground of the attack. —Sir William Thomson.