The divisions of the scale can be carried beyond the fixed points, if requisite, by equal graduations. Fahrenheit's scale is very convenient in some respects. The meteorological observer is seldom troubled with negative signs, as the zero of the scale is much below freezing. Again, the divisions are more numerous, and consequently smaller, than on other scales in use; and the further subdivision into tenths of degrees, seems to give all the minuteness usually required. _Celcius_, a Swede, in 1742, proposed zero for the freezing point, and 100 for the boiling point, all temperatures below zero being distinguishable by the sign (--) minus. This scale is known as the _centigrade_, and is in use in France, Sweden, and the southern part of Europe. It has the advantage of the decimal notation, with the embarrassment of the negative sign. _Reaumur_, a Frenchman, proposed zero for the freezing point, and 80 deg. for the boiling point, an arrangement inferior to the centigrade. It is, however, in use in Spain, Switzerland, and Germany. It is merely a simple arithmetical operation to change the indications of any one of these scales into the equivalents on the others. To facilitate such conversions, tables are convenient, when a large number of observations are under discussion; and they can be easily formed or obtained. In the absence of such tables, the following formulae will insure accuracy of method, and save thinking, when occasional conversions are wanted to be made:--F. stands for Fahrenheit, C. for Centigrade, and R. for Reaumur. Given. Required. Solution. F. C. = (F.-32) 5/9 F. R. = (F.-32) 4/9 C. F. = 9/5 C. + 32 C. R. = 4/5 C. R. F. = 9/5 R. + 32 R. C. = 5/4 R. _Example._--Convert 25 deg. of Fahrenheit's scale into the corresponding temperature on the Centigrade scale. Here C. = (25 - 32) 5/9 C. = -35/9 = -3.9 or nearly 4 deg. _below_ zero of the Centigrade scale. The algebraical sign must be carefully attended-to in the calculations.