The chart is drawn for midsummer and midwinter day on the 40th degree
of north latitude, which is taken as the best average line that runs
midway of the country from ocean to ocean, passing through or near New
York City (N); Philadelphia, Pa; Columbus and Cincinnati (S), Ohio;
Indianapolis, Ind. (S); Springfield, Ill. (S); St. Louis and Kansas
City, Mo. (S); the northern boundary of Kansas; Denver, Colo. (S); Salt
Lake City, Utah (N); Carson City, Nev. (S); and Sacramento, Calif. (S).
With the exception of St. Louis and Sacramento, which are something
over a degree south of this line, all of these places are either on it
or within less than a degree of it, north or south.
[Illustration: