In 1714 a German glassblower and amateur physicist named Gabriel Fahrenheit (1686-1736) made a gadget that would indicate how hot or cold an object was by how far up or down a thin column of mercury inside a glass tube would expand or contract as its temperature changed.

To put numbers on it, he decided that there should be 180 “degrees” between the freezing point and the boiling point of water. Then he made up a batch of the coldest concoction he could create, a mixture of ice and ammonium chloride, and called its temperature zero.

When he stuck his gadget into freezing water, the mercury went up 32 degrees higher than that. Since boiling water was to be 180 degrees higher than that, it came out to be 212. And that’s how we got those crazy numbers, 32 and 212.

Six years after Fahrenheit himself cooled to room temperature, a Swedish astronomer named Anders Celsius (1701-1744) decided that it would be more convenient if there were only 100 “degrees” between the freezing and boiling points of water. So he set the freezing point at zero and the boiling point at 100. And that’s how we got the Celsius scale of temperatures.

Every chance I get, I lobby for a little-known, simple method of conversion between Fahrenheit and Celsius temperatures. (And yes, it’s in all my other books, and I’ll keep doing it until everybody gets it right!) Forget those confusing formulas you learned in school.

(Do you add, or is it subtract 32 before, or is it after, multiplying, or is it dividing, by 5/9? Or is it 9/5?)

My way is as easy as 1-2-3:

(1) Add 40 to the number you want to convert (either F or C).

(2) Multiply or divide the result by 1.8.

(3) Subtract 40.

That’s it. All you have to remember is the fact that Fahrenheit temperatures are always bigger numbers than their Celsius equivalents, so you multiply by 1.8 to convert from C to F, and you divide by 1.8 to convert from F to C.

And that’s just what you expected it to be, right?