We have become accustomed to the pressure of the atmosphere in which we live and fail generally to realise the latent power it represents. But we have a simple means of recalling it to mind. If we consider a mountain lake, its waters also represent potential energy. To release this energy, all that need be done is to install a suitable plant (a hydro-electric station) at a lower point, where the waters of the lake exercise considerable pressures which can be utilised in work. In the same way, to “awake” atmospheric energy, it suffices to provide a source of low pressure (a vacuum unit) in relation to which the atmosphere acts as an infinite reservoir of compressed air.