The lightness of the moving part enables great rapidity of action to be obtained, which for fast speed working is very essential.
The galvanometer which is used for ballistic observations should have a somewhat heavy needle with a period of vibration of not less than five seconds, so that the transient current may have ceased before the swing has well begun; an instrument of the d'Arsonval form is recommended, not only because it is unaffected by outside magnetic influence, but also because the moving part can be instantly brought to rest by means of a short-circuit key, thus effecting a great saving of time when a series of observations is being made.
For some people, moving part of the house at a time isn't possible.
Simply put, there's a fundamental lack of recognition of your presence other than as a moving part of the furniture.
