What form of figurative language is used here? ?

in those days the church was not merely a thermometer (strictly tells the temperature) that recorded the ideas and principles of popular opinion; it was a thermostat (changes the temperature) that transformed the mores of society.

the scene now shifts back to the shelby plantation in kentucky, where  aunt chloe  has just received the letter tom wrote her with little eva's . mrs. shelby tells her husband about the letter, in which tom says that although his new family is kind, he still longs to return to his "real home."

mr. shelby, in the meantime, has still been plagued by debt. mrs. shelby offers to raise money, especially so that they can buy tom. mr. shelby becomes angry, and his wife lets the unlikely hope drop for the present. chloe then calls for mrs. shelby and asks if she could be hired out as a pastry cook in louisville in order to earn money for tom. mrs. shelby gives chloe her blessing.