Lash-up electrical Circuit Breaker in wooden box with glazed lid. System incorporates an electro-magnet (coiled wire around soft iron core) and two glass pots containing mercury to make the electrical connection and a Mica condenser marked PRO PAT 20287-30 British made Telsen Electric Ltd. Possible used with an electrically heated thermostatic water-bath. Date of Mica Condenser (from provisional patent) 1930. Approx date of Circuit breaker 1930