Events
| Crime/Disasters | Eight men die in a mining disaster in south-west England. | 05/12/1866 |
| Legal/Political | The first session of the 39th Congress is sitting in Washington DC from early January to late July, 1866 |
01/07/1866 to 07/27/1866 |
| Science/Technology | The Washington Observatory observes a new variable star flaring in the Coronae Borealis | 05/12/1866 |