Since the sea breeze is caused by the temperature difference between the air over land and that over water, its intensity might be expected not only to increase while the temperature difference increases to its maximum but also to continue increasing until the difference decreases to zero. It is shown that in a model taking friction into account the intensity of the sea breeze begins to decrease considerably earlier, in better agreement with the observations. The diurnal rotation of the sea breeze can be explained as an effect of the Coriolis force. The observations of the diurnal variations of the sea-breeze direction made at Boston agree reasonably well with the theory, especially insofar as the modifying effects of a superimposed general wind are concerned. Abstract Since the sea breeze is caused by the temperature difference between the air over land and that over water, its intensity might be expected not only to increase while the temperature difference increases to its maximum but also to continue increasing until the difference decreases to zero. It is shown that in a model taking friction into account the intensity of the sea breeze begins to decrease considerably earlier, in better agreement with the observations. The diurnal rotation of the sea breeze can be explained as an effect of the Coriolis force. The observations of the diurnal variations of the sea-breeze direction made at Boston agree reasonably well with the theory, especially insofar as the modifying effects of a superimposed general wind are concerned.