As a result, Prof. Thomson devised a compass-card which is remarkable for its lightness and sensitiveness. It is made of two sets of magnets, containing four needles each, arranged symmetrically on the right and left of the pivot. The four needles, forming a set, are of unequal length, ranging from 3-1/4 to 2 inches, with the shortest outermost. Such a card, with its associated correctors of steel magnets and soft-iron balls, has added greatly to the safety and certainty of navigation; and as such, it is used to-day in the merchant service and in the navies of most countries of the world. As we have seen, Thomson had the keen, racy wit of his race. Lecturing before the members of the Birmingham and Midland Institute in 1883, he placed himself and his nationality on record in a very humorous way. His subject was "The six gateways of Knowledge." As will be remembered by the readers of _The Pilgrim's Progress_, old Bunyan likened the soul to a citadel on a hill having no means of communication with the outer world save by live gates, _viz._, the eye gate, the ear gate, the mouth gate, the nose gate and the feel gate. These are the five senses by which we obtain our knowledge of the material world which surrounds us. But Prof. Thomson took issue with Bunyan, with Reid, and the metaphysicians of all time in maintaining in this lecture that we have six gateways of knowledge instead of five, justifying the position which he took by affirming that the sense of touch is really twofold, one of heat and the other of force. It does not appear, however, that he made any marked impression on the philosophic thought of the day, for psychologists continued to write with undisturbed equanimity of the five senses and not the six. It was on this occasion that Prof. Thomson said: "The only census of the senses, so far as I am aware, that ever before made them more than five was the Irishman's reckoning of seven senses. I presume the Irishman's seventh sense was common sense; and I believe that the possession of that virtue by my countrymen, _I speak as an Irishman_, I say the large possession of the seventh sense which I believe Irishmen have, will do more to alleviate the woes of Ireland than the removal of 'the melancholy ocean' which surrounds its shores."