The electroscope is an instrument that allows to determine the presence of electrical charges.
A simple electroscope consists of a vertical metal rod that has a ball at the top and two very thin sheets of gold at the opposite end. The rod is supported on top of a clear glass case with a metal frame in contact with the ground. When an electrified object is brought closer to the sphere, the rod becomes electrified and the lamellae charged with the same sign as the object repel each other, their divergence being a measure of the amount of charge they have received. The electrostatic repulsive force is balanced by the weight of the blades. If the object is moved away from the sphere, the plates, losing polarization, return to their normal position.
The first electroscope was created by the English physician William Gilbert to conduct his experiments with electrostatic charges. Currently this instrument is nothing more than a museum curiosity, giving way to better electronic instruments.
This allows us to obtain energy spectra like those of JS9
A photometer is any device that helps us measure the intensity of light and this, obviously, is something fundamental for photography. There are basically two different types of photometer: the incident light photometer and the reflected light photometer. Each of them has its specific applications and uses. This gives us the photometries.
Regarding these, I have to say that I have not analyzed what type of elements they are equal to since it would not be exact. When it comes to knowing the chemical element, there are many variables which I do not know so I thought it would be better to leave them as is.