Halliday & Matthiessen (1999: 543-4):
There are similar contexts [in Newton's Opticks] for expressions such as an inequality of Refractions, the impinging of Light on ... Bodies, the thickness of the Body, reflecting power in the passages cited above. The nominalised forms inequality, impinging, thickness are not technical terms; or rather, they are so to speak technicalised for the given instance, but they do not lose their semantic status as property or event. Why then are they reconstrued as nouns?The reason is to be found in the grammar of the textual metafunction. In order to function with the requisite value in the message, which means either as Theme or as focus of information, they cannot remain as complete clauses; they have to be "packaged" into single elements of clause structure, and the only available constituent for this purpose is the nominal group. Instead of being a process in its own right, light impinges on a body, the phenomenon in question is construed as a participant, the impinging of light on a body. It can then take on a clearly defined status in the grammatical construction of the discourse.
What is beginning to emerge here is a grammar for experimental science: a way of construing experiential meaning so that it can be organised textually into a form of discourse for the advancement of learning.