Immediately after receiving this letter, I made some experiments as
follows: I took a green, forked twig, and found that over iron
water-pipe, gas-pipe, and over a cistern of water, it turned down
vigorously. I then took a wet rag and fastened it on top of the twig
or rod. As Mr. Sangster testifies, I found it powerless over the iron
water-pipe and over the gas-pipe, but it turned rapidly over the
cistern. I put a key on the end of the rod over the wet rag; then the
rod turned over both iron pipes promptly. Again, I took off the rag
and put the key on the rod, and walking to the cistern, found that
there was no movement. I took off the key and the rod turned
instantly. I have no doubt but that he is correct as regards other
metals.