The Fahrenheit scale was originally calibrated to three points. The first point was set at 0 °F and measured from the lowest temperature of a mixture of water, ice and ammonium chloride at equilibrium. The second point was measured when still water would start to form ice on its surface and assigned the value of 32 °F. The third point was set to 96 °F and is recorded by measuring the temperature of a person when the thermometer is held under the armpit or under the tongue. He designated the interval of a degree Fahrenheit to correspond to 64 degrees between the second and third point. This made marking his thermometer easy since he could bisect the interval between the two values six times.
Scientists later observed that water would boil at nearly 180 degrees above its freezing point. The scale was modified to make this value exactly 180 degrees. This set the temperature of water to 212 °F. This slight alteration moved the body temperature reading to 98.6 °F that we know today.
Find out what else occurred on this day in science history.
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