Halliday & Matthiessen (1999: 542-3):
When we come to the writing of Newton, however, we find formulations such as the following:… by these two Experiments it appears, that in equal Incidences there is a considerable inequality of Refractions.
… the cause of Reflexion is not the impinging of Light on the solid impervious parts of bodies, but .. .
… if the thickness of the body be much less than the Interval of the Fits of easy Reflexion and Transmission of the Rays, the Body loseth its reflecting power.These contain a great deal of grammatical metaphor, contrast them with more congruent forms of expression such as
light is refracted unequally (even) when it falls at the same angle;light is reflected not because it impinges on the solid, impervious parts of bodies';if the body is much less thick than the interval between the points where the rays are easily reflected and (where they are easily) transmitted, the body is no longer able to reflect (light).
Why has the mode of expression changed along just these lines?