Examples of mysteries explained *away*

I am look­ing for ex­am­ples of mys­te­ri­ous an­swers that were even­tu­ally ex­plained *away* by sci­ence. I can think of two: One is the be­lief that the be­havi­our of liv­ing things was ex­plained by the mys­te­ri­ous force of elan vi­tal, and not by mere chem­istry; which was de­stroyed by the syn­theti­sa­tion of urea. The other is the spe­cial (and mys­te­ri­ous) role of the con­scious ob­server in quan­tum me­chan­ics, which was ex­plained away by demon­strat­ing that rocks can get en­tan­gled with elec­trons just as much as brains can. Can any­one fur­nish me with other ex­am­ples?

I ob­serve in pass­ing that phlo­gis­ton is *not* such a mys­te­ri­ous an­swer. Eliezer is down on it, but I think un­justly so; for peo­ple did in fact perform ex­per­i­ments on phlo­gis­ton, in­clud­ing the fi­nal ex­per­i­ment to find the weight of the phlo­gis­ton that had passed out of the burn­ing ma­te­rial and into the byprod­ucts. It turned out that the phlo­gis­ton had nega­tive mass… in other words, that the di­rec­tion of the trans­fer had been misi­den­ti­fied. But if you think of phlo­gis­ton as `nega­tive oxy­gen’, it makes the same pre­dic­tions as mod­ern chem­i­cal the­ory. This is no worse a mis­take than mis­tak­ing the di­rec­tion of the cur­rent, a mis­take which is *still* en­shrined in our sign con­ven­tions; it is not a mys­te­ri­ous an­swer of the form “X->Y” with no de­tails of X given and any value al­lowed for Y.

How­ever, I digress. Mys­te­ri­ous an­swers blown away by ex­per­i­ments, any­one?