Abstract: A thermal regulator stabilizes the temperature within an internal cavity of an instrument. The thermal regulator includes a circulator that draws ambient medium surrounding the instrument and recirculated medium within the internal cavity, into a duct. The circulator forms a mixture of the drawn ambient medium and recirculated medium. An adjustable heater intercepts the mixture and controls the temperature of the mixture to be within a temperature range that is less than a temperature range of the ambient medium in which the instrument is surrounded.