But in 1933 it is almost startling to find that Leslie argued from observations with his photometer that bodies are, or matter is, so diffuse that the ultimate particles "may bear no sensible proportion" to the space which they occupy.
In its widest sense, a photometer is an instrument for measuring light intensity or optical properties of solutions or surfaces. Photometers are used to measur:
- Light absorption
- Scattering of light by media
- Reflection of light