Here was revealed to the Sidralmo the path they had to follow; a wide vista into the darkness had been suddenly opened. It was not long before they had taken full advantage of the discovery. They invented the most helpful of all their instruments, the sidralan or biometer; they hung the combination of life-sensitive plant and nerve-sensitive metal itself in a vacuum, directly in the path of an electric current; the details of its mechanism they rapidly improved till it measured with accuracy the degree of vitality in any plant or animal. But they soon found that it was differently affected by vegetable and animal life. The energy of the former moved it but slightly, and only in certain directions; the latter seemed to surround it and agitate it from all sides; it quivered as if with subdued excitement. Yet there were degrees in both; some plants moved it more than the most primitive unicellular animals, although the movement was less pervasive. Thus were they well on the way towards the isolation of the life-principle from its constant concomitants. The biometer came to be of as much importance to the medical superintendents as to the Sidralmo; it abridged the labour of their weekly inspection; for it told in a moment whether the vitality in any member of the community had fallen or risen in degree, whether it was below the proper average, in short whether all his organs and tissues would have to be minutely examined for the cause, and whether his dietary scheme would have to be revised. The psycho-physiological families found it of some use in their investigations into the faculties of man and their basis in his bodily constitution. They found that the wiser and more intellectual a personality was, the more gently he moved the sidralan; the more of animal vitality he had, the more violently he agitated it by his presence. But the instrument was too rough and undiscriminating for their purposes. It could not distinguish between the purely spiritual and the purely animal except in this loose way. They tried modifications of it, but without success. It was the Ailomo or astrobiological families that helped them to take the right direction. They were constantly bringing down out of the stratum above the atmosphere vessels full of the seeming nothingness that existed there, in order to investigate it and see whether it was mere vacuum or not; and though the contents appealed to none of their senses but the electric, their various instruments of research revealed different energies and a large amount of life, besides minute forms of matter without life. On several occasions they had noticed that the contents affected their tests differently when the experimenter was near and when he stood at a distance. Step by step they separated the element that acted thus from its various concomitants. And soon they were able to concentrate a considerable quantity of it in a receiver exhausted of air, and to precipitate it in powdery metallic form.