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Old 07-08-2012, 11:19 AM
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lamare lamare is offline
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Anyone feels like repeating Wheatstone's 1834 experiment to disprove Einstein?

As I posted on the Gray tube thread, Wheatstone's 1834 experiment could be pretty easily repeated with modern electronics.

Tuks Unsorted KieknWatTWordt Stuff : Wheatstone Experiments To Measure The Velocity Of Electricity

It is a very interesting experiment. Very cool how he managed to measure the rotation speed of his shaft:

It was a point of essential importance to determine the angular velocity of the axle carrying the mirror. No confidence could be placed in the result obtained by calculating the train of wheels, as in such rapid motion many retarding causes might operate and render the calculation uncertain : it was necessary, therefore, to devise a means independent of these sources of error, and which should immediately indicate the ultimate velocity. Nothing appeared more likely to effect this purpose than to attach a small syren to the instrument, the plate of which should be carried round by the axle of the mirror. [...] The difficulty was at last overcome by employing the arm Q itself to produce the sound. A small slip of paper was held to it ; and as at every revolution a blow was given to the paper, its rapid recurrence gave rise to a sound the pitch of which varied with the velocity of the motion. When the machinery was put in motion with the maximum velocity I employed in my experiments, the sound G#4 was obtained, indicating 800 revolutions of the mirror in a second. I am not aware that anything can have interfered with the accuracy of this result ; the same sound was heard when different pieces of paper or card were used ; and on moderating the velocity, the sound descended through all the degrees of the scale below it, until distinct percussions were perceived.
That is just awesome!

Anyway, I studied this article a while back and there is an important detail: you have to take into account the fact that the current, shockwave or whatever it is, is balanced. You get one pulse traveling from the positive pole of the HV cap/coil, and one from the negative. So, if you would only take two spark gaps at the begining and at the end of the long wire, your gaps would fire simultaneously. Wheatstone already thought of that, too:
But as it is only on the hypothesis of an actual transfer of a fluid from one end of the wire to the other that a difference of time between the two sparks at its opposite extremities might be expected to be observed, in order to render the proposed experiment independent of this theoretical view, I took the necessary precaution of bringing a third spark, formed by disconnecting the middle of the wire, near to and in a line with the extreme sparks. For on the supposition of the transfer of two fluids in opposite directions, the extreme sparks would be simultaneous, but the middle spark later in its occurrence; the same appearances would also accord with the theory of one electricity, if we admit that a disturbance of electric equilibrium is simultaneously propagated from each end, arising in the one case from successive additions to, and in the other from successive subtractions from, the neutral quantity in the conducting wire.
So, I made a drawing of how this experiment could be repeated pretty easily with a decent scope and a handful of standard components.

It's a matter of mounting three spark plugs in light-tight enclosures together with photo transistors and measuring the time it takes for a pulse to propagate along a long wire using a scope:

Originally Posted by lamare View Post
Some time ago, I thought about re-doing Wheatstone's experiment with modern equipent, which shows you schematically what Wheatstone was doing:

High res:
The idea is that when using photo transistors, you don't need a rotating mirror. Just three spark gaps with three photo detectors in order to detect the moment of sparking.

You may need pretty fast photo transistors or use photo diodes or something, but OTOH the switch-on times are not critical, as long as the response delays on the three different sensors are (almost) the same, which means the connection from transistor to scope should have the same length for all three transistors.

For insulators, one could use the kind of insulators used by farmers:

In principle I can do it myself, but I only have a 10 MHz scope, so I would need about 600 meters of wire. With a 300 MHz scope, one could do with as little as 20 meters of wire, which is a bit more practical...

If this experiment is pulled off succesfully and achieve the expected result, namely the measurement of a propagation speed of about 1.5 times the speed of light, you would probably get your name in the history books as having performed the single experiment with which Einsteins theory has been proven wrong.

Last edited by lamare; 05-24-2013 at 07:26 AM. Reason: typo
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