In what appears to have now become a fully-fledged series, The Perth Mint's line of innovative, "insert" coins now has a new instalment! Beginning in 2015 with an Alice in Wonderland coin bearing a working clock, followed by the 2016 Yin Yang charm, and the 2017 Compass coin, this loose series now includes a Thermometer!
Historically, the Aztecs were one of the many that worshipped the changing temperature; More specifically, Itztlacoliuhqui, the god of frost and cold, and Tonatiuh, the Sun god.
Surrounded by Aztec symbols and designs, the central Thermometer actually works, and features both Celsius and Fahrenheit scales! Every other coin in this "series" has sold out and, with a mintage of just 2,500 pieces, this 2oz pure silver thermometer issue must surely go the same way.