As all the rest of the circuit was kept absolutely the same in the two different sets of experiments, these results conclusively prove that the responsive electro-motive variation is solely due to the molecular disturbance produced by mechanical vibration in the acted wire. A new and theoretically interesting molecular voltaic cell may thus be made, in which the two elements consist of the _same metal_. Molecular disturbance is in this case the main source of energy. A cell once made may be kept in working order for some time by pouring in a little vaseline to prevent evaporation of the liquid. It will be shown further, in succeeding chapters, by numerous instances, that any conditions which increase molecular mobility will also increase intensity of response, and conversely that any conditions having the reverse effect will depress response. CHAPTER XII INORGANIC RESPONSE--METHODS OF ENSURING CONSISTENT RESULTS Preparation of wire--Effect of single stimulus. I shall now proceed to describe in detail the response-curves obtained with metals. The E.M. variations resulting from stimulus range, as has been said, from .4 volt to .01 of that value, according to the metal employed. And as these are molecular phenomena, the effect will also depend on the molecular condition of the wire. #Preparation of wire.#--In order to have our results thoroughly consistent, it is necessary to bring the wire itself into a normal condition for experiment. The very fact of mounting it in the cell strains it, and the after-effect of this strain may cause irregularities in the response. For the purpose of bringing the wire to this normal state, one or all of the following devices may be used with advantage. (1) The wires obtained are usually wound on spools. It is, therefore, advisable to straighten any given length, before mounting, by holding it stretched, and rubbing it up and down with a piece of cloth. On washing with water, they are now ready for mounting in the cell. (2) The cell is usually filled with tap-water, and a period of rest after making up, generally speaking, improves the sensitiveness. These expedients are ordinarily sufficient, but it occasionally happens that the wire has got into an abnormal condition. [Illustration: FIG. 58.--EFFECT OF ANNEALING ON INCREASING THE RESPONSE OF BOTH A AND B WIRES (TIN) Stimuli (vibration of 160 deg.) applied at intervals of one minute.]