The March 29 2006 solar eclipse as detected by a vibrating tuning fork

At the occurrence of the March 29 2006 solare eclipse, I' ve been measuring the period of a massive electrically maintained 50 Hz tuning fork.

It appeared that just before eclipse start the period has been disturbed as shown in this chart, which covers 36 hours:

The measurement has been made to a resolution of 100 picoseconds using a lab grade timer-counter with high stability time base reference (better than 5 x 10e-10). The test has been made in my unattended lab in a quite quiet area, about one meter below the level of the surrounding soil, the entire equipment being well stabilized by more than 20 days of continuous operation. The fork was running in open air, and the above curve is the result of a correction for atmospheric pressure. The following chart shows the uncorrected data (72 hours):

The x axis shows UT (local solar time is UT+1). The y axis shows the measured period in microseconds. The red curve (pressure) has been linearily scaled and its vertical span is about 10 millibar.

Here is a detailed picture of the fork:

It was made in England in 1962 by Bryans Aeroquipment Ltd., and was termed "low temperature coefficient transistorized tuning fork". The fork itself is secured to a heavy steel plate and forms the resonant element of a closed loop amplifier, and this ensures a stable continuous oscillation. In my setup I've excluded the built-in power supply and the small bulb, and I used a precision external power supply having an oven controlled voltage reference. In the picture below the fork is shown in the operating position:

The fork is in that position since October 2005 and has been keept undisturbed. The marble block weights some 40 Kg and along with the foam layers serves to isolate the fork from the already quiet environment.

Comments:

in preparation.......