Note 2 — I. METEOROLOGY AND CLIMATOLOGY.
Reading edition
For comparison of scales see Table XXVI., Vol. I., p. 333.
To convert Centigrade readings into Fahrenheit the rule is “Multiply by 1.8 and add 32.” This can be done mentally in a moment, thus: “Multiply by 2, subtract one-tenth of the product, and add 32.” E.g., to convert 10° C. to F.: 10 × 2 = 20; one-tenth of 20 = 2; 20 - 2 = 18; 18 + 32 = 50° F.