Secondary Circle. Any great circle whose plane is perpendicular to a primary circle. It follows that a secondary circle will contain the axis and poles of the primary; and that the primary will contain the axes and poles of all its secondaries.
Secondary Cold Front. Front of polar air following first cold front.
Secondary Depression. Second area of low pressure formed inside a meteorological depression. Generally moves round primary depression, and may combine with it.
Secondary Port. Port, or position, whose tidal phenomena are deduced by reference to tides at an appropriate standard port.
Second Class Paper.Written undertakings to pay, whose financial value is open to doubt. Second Differences. Differences that affect a primary difference when the variation in value of a quantity is not uniform.