I n some coobustion systems, particularly aemengines fitted with reheat or afterburner units, there arises from causes unhmin a cxclic inatability bwn colloquially as' buzz'. In CB~ C'P where this is uncontrolled it my reach. lestructive severity and hence it is of some'importance to understand and reduoe its occurrence. The phenomenon has been investigated in situations where it has been a problem but has appeared very complicated. a small rectangJlar rig was usllufactured with provision for several typs of instxcentation appropriate to the visualisation and meaurement of time varying quantities within the rig.