Gravitational lensing: a unique probe of dark matter and dark energy — Philosophical Transactions A

Gravitational lensing: a unique probe of dark matter and dark energy — Philosophical Transactions A: "William Wallace Campbell, Director of the Lick Observatory, was likewise motivated to test Einstein’s theory (although perhaps more sceptically than Findlay-Freundlich). He was also unfortunate in 1914; as a US citizen he was free to leave Russia but his equipment was impounded. At a subsequent eclipse in Washington State in 1918, Campbell had to make do with inferior equipment and eventually concluded that there was no deflection. He was poised to publish his rejection of Einstein’s theory when he heard of Eddington’s likely verification during a visit to London in 1919. In a famous telegram, he urged his Californian colleagues to hold off submitting the paper."