The surface of rock or soil, newly-exposed, for example, by tunnelling, and having the tendency to become friable on exposure to the atmosphere, can be protected by forming thereon a film by the process of combining on the surface at least one coagulable material and a coagulating agent therefor. The actuator includes a cylindrical pin; a cylindrical closed chamber; a biasing member; a permanent magnet; a coil housing; and a coil supported by the coil housing. The scratch determination unit determines that predetermined sectors are affected by a single continuous scratch if the predetermined sectors are defective and a distance therebetween is not larger than the length of a single continuous scratch. The system can include an interaction controller, which sets a duration of time for the users to communicate in a dialogue environment. The rotatable stirrup bar allows the stirrup leathers to rotate relative to the saddle with reduced wear and tear to the stirrup leather.