Crook's Radiometer apparatus mounted on a sturdy plastic molded base. Comprised on an evacuated glass bulb with black and white veins. Comprised on an evacuated glass bulb with black and white veins. Each vein has a blackened side and the reverse side is bright. 2.75" (70mm) diameter at the widest point, containing a fine pivot which supports four light weight metal arms. Apparatus stands 7" tall. Crook's Radiometer apparatus mounted on a sturdy plastic molded base. Comprised on an evacuated glass bulb with black and white veins. Comprised on an evacuated glass bulb with black and white veins. Each vein has a blackened side and the reverse side is bright. 2.75" (70mm) diameter at the widest point, containing a fine pivot which supports four light weight metal arms. Apparatus stands 7" tall.