Many writers use continuous and continual interchangeably. These words have different, distinct meanings. Continuous refers to something that occurs for a period of time without interruption (e.g. that is constant). Continual refers to something that occurs over a period of time with interruption (e.g. that is periodic). I remember the differences between these two terms through references to water.
The tap continually dripped. The water, however, continuously ran through the hose.
Drips aren’t constant, they come at intervals, so the word continual is applicable. Water running through a hose, however, is constant and, therefore, continuous is the appropriate word.