It may be well to refer for a moment to the variations in temperature known as inversions. In the accompanying diagram it will be seen that the temperature falls with elevation, and starting from the ground on a day when the temperature is near the freezing point, 273 degrees A., one finds at a height of seven thousand meters a fall of about forty degrees. It is not easy to represent on a single diagram the variation in detail and therefore we have divided the air column into three parts, the scales being as one to a hundred. The right-hand diagram shows the gradual rise in temperature for a height of one meter and the peculiar inversion that occurs a few centimeters above the ground. Unfortunately it is in this layer where detailed temperature observations are most needed that our instruments are least satisfactory. Ordinary thermometers can not be relied on for such small differences and the exploration of this stratum by self-recording instruments is difficult. In the middle diagram is shown the temperature gradient at times of frost, from the ground to a height of one hundred meters. It will be seen that at a height of fifty meters the temperature may be ten degrees higher; and in general the rise continues with elevation. A good illustration of a valley inversion is given by the chart of May 20, in which continuous records for three levels, 18, 64 and 196 meters above sea level, are given. At such times fruit or flowers on hillsides escape damage from frost while in all the depressions and low level places the injury may be marked. These differences in temperature are not at all unusual and may be anticipated on clear, still nights during spring, fall and winter. Clouds or a moderate wind will prevent such an inversion. We shall refer again to this in speaking of the cranberry bogs of the Cape Cod district and the frost warnings issued from Blue Hill Observatory. The great inversion in the atmosphere, however, is that which we have indicated as occurring at the height of nine thousand meters. Above this, the temperature ceases to fall and we enter what has been called the stratosphere or isothermal region. For convenience we will call this upper change the MAJOR inversion and the lower one near the ground the MINOR inversion. In some ways we know more about the former than the latter. Strictly speaking, the minor inversion is the chief factor in determining local climate since it controls night and early morning temperatures and in large measure the early or late blooming of flowers and ripening of fruits.