It is a generally accepted fact that large bodies of water exert a decided influence on the climate and on the cultural development in the immediate vicinity. Just how much and at what times this influence is most felt has always been more or less a matter of conjecture. There are many variables which force themselves into the picture to the extent that it is difficult to determinate which one is at work at a particular time. Among these variables might be mentioned distance from the lake, elevation of land above the lake, angle of incidence of the sun's ray, percentage of cloudiness, and wind directions.
Among the many climatic factors, such as snowfall, barometric pressure, wind direction and cloudiness, perhaps the most discussed and the one which effects more people directly is temperature. It was therefore thought best to represent those phases of temperature in a graphical way so that its effects could be seen in a quantitative way as well as in a qualitative way. The series of maps and graphs included in this paper illustrate just when and to some degree how much the lake influences the temperature of the surrounding land area. The limitations placed on the "how much" part of the preceding statement are necessary because of the many other factors entering to affect the temperature at the same time the lake is casting its influence.