On the Free Vibrations of a Lecher System Using a Lecher Oscillator

F. C. Blake, Charles Sheard
1911 Physical Review  
T WO forms of Lecher system were employed; one after the manner of Lecher, using 5 cm. plates attached to the oscillator circuit and 3 cm. plates connected to the wire system proper. A second form, consisting of cylinders, cone-shaped at one end, was used as a part of the oscillator circuit; this allowed the coupling of the two circuits to be readily changed. A similar device was made use of at the bolometer end of the circuit. A check receiver, of constantan-iron wires, shunted through a high
more » ... ted through a high resistance across the spark-gap in oil, was employed for the purpose of checking the energy delivered to the Lecher circuit. By its use it was possible to check readings at any given point on the system to within 1 per cent, at any time. The main points of the work as presented were: 1. A first approximation of the ideal case as to the distribution of energy as given by Abraham 2 was obtained. The theory was found to hold for the first, the third (2 per cent, error due to experimental errors) and the second harmonics, these last being in error by 8 per cent, due to the influence of the oscillator vibrations also imposed upon the system. 2. The ideal case ceases to be such just in proportion as the bridge length is more and more comparable to the Lecher wire length. Curves for 2, 5 and 11.5 cm. distance between parallel wires were shown; for this last distance the vibrations ceased to be of a simple nature. 3. It is known theoretically 3 that such a system has two superimposed oscillations; those due to the oscillator and those which are the free vibrations proper. The effect of coupling (using the second form of coupling and check receiver) on each of the sets of vibrations was investigated. It was found that any particular overtone could be strengthened by so varying the coupling that the oscillator vibrations fell in unison with it. 4. It was found that for bridge lengths small in comparison to the Lecher wire length the currents behaved as if they were longitudinal and not transverse. The proof of this is based upon an experimental verification of Abraham's 4 theoretical considerations that for longitudinal currents the potential varies as the logarithm of the distance from the wire. 5. The Kirchhoff-Abraham generalization of the Thomson formula 5 was verified to within 1 per cent, in the cases where the tones were strictly harmonic. Abstract of a paper presented at Abstract of a paper presented at
doi:10.1103/physrevseriesi.32.235 fatcat:dlhherho5ncpbkldgx2dt2tjxi