Perhaps you can see the relation, Robert, which they bear to each other ?" "No, I cannot say that I do." Robert had sat listening to this strange statement with parted lips and staring eyes.
"I will show you.

Speaking atomically, bismuth is the heaviest of the metals.

Its atomic weight is 210.

The next in weight is lead, 207, and then comes mercury at 200.

Possibly the long period during which the current had acted in my absence had reduced the bismuth to lead and the lead in turn to mercury.