What Are The Uses Of Six's Maximum And Minimum Thermometer?

Six's maximum and minimum thermometer is a popular thermometer among gardeners for use in greenhouses. Its purpose is to record the maximum and minimum temperatures reached since the thermometer was last read. Generally speaking a minimum temperature occurs during the night and a maximum during the day. It was invented by James Six towards the end of the eighteenth century, and consists of a fairly large cylindrical bulb full of alcohol, or oil of creosote, connected by a you- shaped stem to a second bulb nearly full of alcohol or oil of creosote. The bend of the you contains a thread of mercury. Two scales are provided, one against each limb of the tube so that the temperature may be read against either of the mercury levels. Resting on each of the mercury surfaces are small steel indexes provided with light springs to hold them in position in the stem. Expansion or contraction of the fluid in the larger bulb causes a movement of the mercury thread. Consequently, one or other index is pushed forward by the mercury and left in the extreme position reached. Thus, the lower end of the index on the left indicates the minimum and that on the right the maximum temperature attained. It is interesting to note that Six's maximum and minimum thermometers were still being used in 2000 of exactly the same design and construction as ones produced over 100 years ago.