MECHANICAL AND ELECTRICAL OSCILLATORS.

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or else he obtains the spring within the chambers of the oscillatoritself. To appreciate the beauty of this it is only necessary to saythat in that disposition, as he showed it, no matter what therigidity of the spring and no matter what the weight of the mov-ing parts, in other words, no matter what the period of vibrations,the vibrations of the spring are always isochronous with the ap-plied pressure. Owing to this, the results obtained with thesevibrations are truly wonderful. Mr. Tesla provides for an airspring of tremendous rigidity, and he is enabled to vibrate bigweights at an enormous rate, considering the inertia, owing to therecoil of the spring. Thus, for instance, in one of these experi-ments, he vibrates a weight of approximately 20 pounds at therate of about 80 per second and with a stroke of about •£ inch, butby shortening the stroke the weight could be vibrated many hun-dred times, and has been, in other experiments.

To start the vibrations, a powerful blow is struck, but the ad-justment can be so made that only a minute effort is required tostart, and, even without any special provision it will start bymerely turning on the pressure suddenly. The vibration being,of course, isochronous, any change of pressure merely produces ashortening or lengthening of the stroke. Mr. Tesla showed anumber of very clear drawings, illustrating the construction ofthe apparatus from which its working was plainly discernible.Special provisions are made so as to equalize the pressurewithin the dash pot and the outer atmosphere. For this purposethe inside chambers of the dash pot are arranged to communi-cate with the outer atmosphere so that no matter how the tempera-ture of the enclosed air might vary, it still retains the same meandensity as the outer atmosphere, and by this means a spring ofconstant rigidity is obtained. Now, of course, tlie pressure ofthe atmosphere may vary, and this would vary the rigidity of thespring, and consequently the period of vibration, and this featureconstitutes one of the great beauties of the apparatus; for, as Mr.Tesla pointed out, this mechanical system acts exactly like astring tightly stretched between two points, and with tixed nodes,so that slight changes of the tension do not in the least alter theperiod of oscillation.

The applications of such an apparatus are, of course, numer-ous and obvious. The first is, of course, to produce electriccurrents, and by a number of models and apparatus on the lectureplatform, Mr. Tesla showed how this could be carried out in