A turbine comprising a first housing having a first shaft rotatably mounted in the housing; a plurality of first spaced apart discs having an outer diameter and mounted on the first shaft and rotatable therewith, each first disc having a radial inner end defining an inner opening, a radial outer end and a pair of opposed surfaces extending therebetween; a second housing having a second shaft rotatably mounted in the housing; and, a plurality of second spaced apart discs having an outer diameter and mounted on the second shaft and rotatable therewith, each second disc having a radial inner end defining an inner opening, a radial outer end and a pair of opposed surfaces extending therebetween, the outer diameter of at least some of the first spaced apart discs is less than the outer diameter of at least some of the second spaced apart discs.