161. Since intervals of time are likewise set and constant, they are also properties of nature; for the duration of a day is constantly twenty-four hours, and the duration of a year is constantly 365 1/4 days. The periods of light and darkness and of warmth and coldness, which cause these intervals to vary in character, themselves recur in constant cycles. The periods which recur in cycles every day are morning, afternoon, evening and night. The periods which recur in cycles every year are spring, summer, fall and winter. The seasons of the year also constantly vary the hours of daylight. Because these periods are not states of life as in the spiritual world, they too are all lifeless. For one finds in the spiritual world a constant light and constant warmth, the light corresponding to the state of wisdom in angels, and the warmth to the state of love, so that the states they pass through are states of life.