fuNE S, I 893J 



NATURE 



•37 



" In presenting these insignificant results I have not attempted 

 I to arrange and coordinate them as would be proper in a strictly 



scientific investigation in which every succeeding result should 



be a logical sequence of the preceding, so that it might be guessed 

 ; in advance by the careful reader or attentive listener. I have 



preferred to concentrate my energies chiefly upon advancing 

 - novel facts or ideas which might serve as suggestions to others, 

 i and this may serve as an excuse for the lack of harmony. The 

 I explanations of the phenomena have been given in good faith, 

 ' and in the spirit of a student prepared to find that they admit 

 ; of a better interpretation. There can be no great harm in a 

 j student taking an erroneous view, but when great minds err, the 



world must dearly pay for their mistakes." 



i The following extracts will serve to show the character of 

 I the discourse : — 



I The Action of the Eye. 



j It can be taken as a fact, which the theory of the action of 

 the eye implies, that for each external impression, that is, for 



'each image produced upon the retina, the ends of the visual 



• nerves concerned in the conveyance of the impression to the 

 mind, must be under a peculiar stress or in a vibratory state. 

 It now does not seem improbable that, when by the power of 

 thought an image is evoked, a distinct reflex action, no matter 

 how weak, is exerted upon certain ends of the visual nerves, 

 and therefore upon the retina. Will it ever be within human 

 power to analyse the condition of the retina when disturbed by 

 thought or reflex action, by the help of some optical or other 

 means of such sensitiveness, that a clear idea of its state might 

 be gained at any time? If this were possible, then the problem 

 of reading one's thoughts with precision, like the characters of 

 au open book, might be much easier to solve than many prob- 



jlems belonging to the domain of positive physical science, in 

 the solution of which many, if not the majority, of scientific 

 men implicitly believe. Helmholtz has shown that the fundi of 

 the eyes are themselves luminous, and he was able to see, in 

 total darkness, the movement of his arm by the light of hi* own 

 eyes. This is one of the most remarkable experiments recorded 

 in the history of science, and probably only a few men could 

 satisfactorily repeat it, for it is very likely that the luminosity of 

 the eyes is associated with uncommon activity of the brain and 

 great imaginative power. It is fluorescence of brain action, as 

 it were. 



Another fact having a bearing on this subject which has pro- 

 bably been noted by many, since it is stated in popular expres- 

 sions, but which I cannot recollect to have found chronicled as 

 a positive result of observation is, that at times, when a sudden 

 ,idea or image presents itself to the intellect, there is a distinct 

 and sometimes painful sensation of luminosity produced in the 

 eye, observable even in broad daylight. 



Two facts about the eye must forcibly impress the mind of the 

 physicist, notwithstanding he may think or say that it is an im- 

 perfect optical instrument, forgetting that the very conception 

 of that which is perfect or seems so to him, has been gained 

 through this same instrument. Firstly, the eye is, as far as our 

 positive knowledge goes, the only organ which is directly affec- 

 ted by that subtile medium, which, as science teaches us, must 

 ili all space; secondly, it is the most sensitive of our organs, 

 mparably more sensitive to external impressions than any 

 '■r. 



This divine organ of sight, this indispensable instrument for 

 thought and all intellectual enjoyment, which lays open to us the 

 marvels of this universe, through whicn we have acquired what 

 (knowledge we possess, and which prompts us to, and controls, 

 all our physical and mental activity. By what is it affected ? 

 ily light! What is light ? 



It is beyond the scope of my lecture to dwell upon the subject 

 i)f light in general, my object being merely to bring presently 

 to your notice a certain class of light effects and a number of 

 phenomena observed in pursuing the study of these effects. But 

 '■'.0 be consistent in my remarks it is necessary to state that 

 Recording to that idea, now accepted by the majority of scientific 

 ;iien as a positive result of theoretical and experimental investi- 

 gation, the various forms of manifestations of energy which were 

 3;enerally designated as "electric " or more precisely " electro- 

 magnetic " are energy manifestations of the same nature as those 

 jf radiant heat and light. Therefore the phenomena of light 

 tnd heat, and others besides these, may be called electrical 

 Phenomena. Thus electrical science has become the mother 

 science of all and its study has become all-important. The day 



NO. 1232, VOL. 48] 



when we shall know exactly what " electricity " is, will chronicle 

 an event probably greater, more important than any other 

 recorded in the history of the human race. 



Transformation of Currents. 



Mr. Tesla then went on to describe the apparatus employed, 

 and the method of obtaining the high potentials and high fre- 

 quency currents which are made use of in his experiments. In 

 order to explain the transformation of currents he used the 

 following analogy : — 



Imagine a tank with a wide opening at the bottom, which is 

 kept closed by spring pressure, but so that it snaps oR suddenly 

 when the liquid in the tank has reached a certain height. Let 

 the fluid be supplied to the tank by means of a pipe feeding at 

 a certain rate. When the critical height of the liquid is 

 reached, the spring gives way and the bottom of the tank drops 

 out. Instantly the liquid falls through the wide opening, and 

 the spring, reasserting itself, closes the bottom again. The tank 

 is now filled, and after a certain time interval the same pro- 

 cess is repeated. It is clear that if the pipe feeds the fluid 

 quicker than the bottom outlet is capable of letting it pass 

 through, the bottom will remain off and the tank will still over- 

 flow. If the rates of supply are exactly equal, then the bottom 

 lid will remain partially open, and no vibration of the same and 

 of the liquid column will generally occur, though it might, if 

 started by some means. But if the inlet pipe does not feed the 

 fluid fast enough for the outlet, then there will be always vibra- 

 tion. Again, in such case, each time the bottom flaps up or 

 down, the sprin? and the liquid column, if the pliability of the 

 spring and the inertia of the moving parts are properly chosen, 

 will perform independent vibrations. In this analogue the 

 fluid may be likened to electricity or electrical energy, the tank 

 to the condenser, tlie spring to the dielectric, and the pipe to 

 the conductor through which electricity is supplied 10 the con- 

 denser. To make this analogy quite complete it is necessary to 

 make the assumption, that the bottom, each time it gives way, 

 is knocked violently against a non-elastic stop, this impact in- 

 volving some loss of energy, and that, besides, some dissipa- 

 tion of energy results, due to frictional losses. In the preceding 

 analogue the liquid is supposed to be under a steady pressure. 

 If the pressure of the fluid be assumed to vary rhythmically, 

 this may be taken as corresponding to the case of an alternating 

 current. The process is then not quite as simple to consider, 

 but the action is the same in principle. 



Electrostatic Force. 



After showing that the human body could be traversed by a 

 powerful electric current vibrating at about the rate of one 

 million times per second, Mr. Tesla said : — 



The amount of energy which may thus be passed into the 

 body of a person depends on the frequency and potential of the 

 currents, and by making both of these very great, a vast amount 

 of energy may be passed into the body without causing any dis- 

 comfort except perhaps in the arm, which is traversed by a true 

 conduction current. The reason why no pain in the body is 

 felt, and no injurious effect noted, is that everywhere, if a cur- 

 rent be imagined to flow through the body, the direction of 

 its flow would be at right angles to the surface ; hence the 

 body of the experimenter offers an enormous section to the cur- 

 rent, and the density is very small, with the exception of the 

 arm perhaps, where the density may be considerable. But if 

 only a small fraction of that energy would be applied in such a 

 way that a current would traverse the body in the same manner 

 as a low frequency current, a shock would be received which 

 might be fatal. A direct or low-frequency alternating current 

 is fatal I think, principally because its distribution through the 

 body is not uniform, as it must divide itself in minute stream- 

 lets of great density, whereby some organs are vitally injured. 

 That such a process occurs I have not the least doubt, though 

 no evidence might apparently exist or be found upon examina- 

 tion. Thesurest to injure and destroy life is a continuous cur- 

 rent, but the most painful is an alternating current of very low 

 frequency. The expression of these views, which are the result 

 of long-continued experiment and observation, both with steady 

 and varying currents, is elicited by the interest which is at 

 present taken in this subject and by the manifestly erroneous 

 ideas which are daily propounded in journals on this subject. 



The electrostatic attractions and repulsions between bodies of 

 measurable dimensions are, of all the manifestations of this force, 



