"The law in question asserts, that the quantity of force which can be brought into action in the whole of Nature is unchangeable, and can neither be increased nor diminished"

This quote by Hermann von Helmholtz is referring to the law of preservation of energy, which mentions that energy can neither be produced nor ruined, but can be transformed from one type to another. This law applies to all types of energy, including mechanical, electrical, chemical, and thermal energy. To put it simply, the total quantity of energy in deep space is constant and can not be increased or reduced. This law is necessary since it helps us understand how energy is moved and transformed in nature. For instance, when a cars and truck is driven, the energy from the fuel is transformed into kinetic energy, which is then utilized to move the cars and truck. This quote by Hermann von Helmholtz is a reminder that the amount of energy in deep space is finite and can not be altered.