They knew that the basis of all scientific advance was accurate measurement. Their old measuring instruments had gradually been overtaken by their own senses, and had to be replaced by others more and more refined. In order to make sure that their senses introduced no personal element into the reports and representations of their various delicate measurers, they had invented an instrument which for fine adjustment surpassed all of these. It was the airolan or sensometer, and by it the medical families in their weekly review of every system in the community were enabled to find the exact personal equation of each. It recorded the upper and lower limit of the various sensations, the limit of endurance, and the vanishing point. Although there was a great evenness in the development of the senses in the community, there was yet considerable variation in the delicacy of perception. One man was keenest in sight, another in hearing, a third in the electric sense, yet there was a certain constancy or proportion in all the senses of every man, a proportion varying according to well-ascertained laws with the hour and the season, the man’s age, and the temperature and health of his body. The airolan tested, measured, and recorded the regular variations of each Limanoran’s senses, and thus he was able to know how far he judged accurately anything he perceived. By its aid he was able to know the exact point at which he would need to call in any one of the various mechanical aids to the senses, the magnifiers, or modifiers, or distance-reducers. By its means they were able to gauge the proper mixture of colours and proper size in architecture that would please at certain distances. By its means, too, they could accurately measure the distance from which any electric or luminous or somniferous impulse had come, when it struck on the senses. It was one of the commonplaces of their policy that whatever could be done by machinery it was waste of skill and energy to do by human labour and thought; and instruments were generally more exact and reliable than the senses and active powers of man, however delicately developed and refined. Of course man’s brain and hand must still guide and superintend all instruments and machinery, but his interference with their automatic working was reduced to a minimum, in order that the discount for personal equation should be as little as possible. It was not, however, so much for the sake of accuracy of result that mechanism was substituted for human work, as for the sake of progress. Every operation and function which could be performed mechanically it was a slur upon human dignity to do; and at once Limanoran humanity was relieved from the necessity, and the freed energy was applied to other and nobler efforts towards progress.