Conversations on Chemistry

This is an excerpt from a book I'm sorta reading now. It was published in 1817, and was a fictional conversation between a teacher and two students, all women, talking about all the new discoveries that had hitherto been made in chemistry. Mrs. B. is explaining the thermometers, and how they differed among different countries.

MRS. B.

The extreme points of the scales are not the same in all thermometers, nor are the degrees always divided in the same manner. In different countries philosophers have chosen to adopt different scales and divisions. The two thermometers most used are those of Fahrenheit, and of Reaumur; the first is generally preferred by the English, the latter by the French.

EMILY.

The variety of scale must be very inconvenient, and I should think liable to occasion confusion, when French and English experiments are compared.

MRS. B.

The inconvenience is but very trifling, because the different gradations of the scales do not affect the principle upon which thermometers are constructed. When we know, for instance, that Fahrenheit's scale is divided into 212 degrees, in which 32° corresponds with the freezing point, and 212° with the point of boiling water: and that Reaumur's is divided only into 80 degrees, in which 0° denotes the freezing point, and 80° that of boiling water, it is easy to compare the two scales together, and reduce the one into the other. But, for greater convenience, thermometers are sometimes constructed with both these scales, one on either side of the tube; so that the correspondence of the different degrees of the two scales is thus instantly seen. Here is one of these scales, (PLATE II. Fig. 1.) by which you can at once perceive that each degree of Reaumur's corresponds to 21⁄4 of Fahrenheit's division. But I believe the French have, of late, given the preference to what they call the centigrade scale, in which the space between the freezing and the boiling point is divided into 100 degrees.

CAROLINE.

That seems to me the most reasonable division, and I cannot guess why the freezing point is called 32°, or what advantage is derived from it.

MRS. B.

There really is no advantage in it; and it originated in a mistaken opinion of the instrument-maker, Fahrenheit, who first constructed these thermometers. He mixed snow and salt together, and produced by that means a degree of cold which he concluded was the greatest possible, and therefore made his scale begin from that point. Between that and boiling water he made 212 degrees, and the freezing point was found to be at 32°.

And so, like the QWERTY keyboard that was a design borne of compromise, the US has lived with the Fahrenheit ever since it was invented. 0 degree Fahrenheit turned out not to be the coldest temperature that could be achieved, the honor of that goes to the Kelvin and it is a temperature that cannot ever be achieved.