Although Dr Duif discounts each of the conventional explanations on its own, he admits that they might, in combination, account for the Allais effect.

ECONOMIST: Gravitational anomalies

Dr Duif has examined various conventional explanations for the Allais effect.

ECONOMIST: Gravitational anomalies

Dr Duif rules out a third explanation, too: that cooling of the Earth's crust due to the eclipse shadow causes the ground to tilt slightly, and thus distorts the results.

ECONOMIST: Gravitational anomalies

Dr Duif also considered the possibility that, because the moon's shadow cools the air during an eclipse, this cooler, and thus denser, air might exert a different gravitational pull on the instruments.

ECONOMIST: Gravitational anomalies

But Dr Duif points out that the anomalous force felt by both Pioneer probes (which are travelling in opposite directions from the sun) is about the same size as that measured by some gravimeters during solar eclipses.

ECONOMIST: Gravitational anomalies