Old navigation papers always have hidden gems in them..
"This training period was marked by only two events of unusual interest. The first was an electric storm which occurred during the 18th trial. Thunder and lightning were almost incessant throughout this trial period. A large tree near the building was shattered by lightning. On this trial there was a great increase in average time, and a slight increase in the average number of errors. The other event, which occurred at the 22nd trial, was an unusually hot day-mercury at 103 F. The rats seemed almost overcome, and, upon being placed in the water, would float for a considerable length of time before starting to swim down the maze pathway. The average time was greatly increased. The errors, however, did not increase appreciably."
Source: The Rôle of Kinaesthesis in the Establishment and Control of the Maze Habit by Sol Evans, @johnwidloski pointed me to it
