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He used an emission spectroscope.

An emission spectroscope heats or otherwise excites an element or compound and then separates the emitted light using a prism or a diffraction grating. If the element is in the gas phase, that is if it's a gas to start with or if it's heated enough to vaporize it, you will see a line spectrum. That means the glowing element emits light only at certain wavelengths.

Line spectra are caused by the excited electrons emitting photons as they drop to lower energy states. So different elements have entirely different line spectra because their electron configurations are different.

Each element has a unique line spectrum and it is by comparing the observed line spectrum with known line spectra that the element can be identified.

I am Christian and I do not consider science and religion as separate. God created the heavens and the earth. There is nothing that is that was not set into motion by God. Religion has to do with how you relate to people and manage the God created universe. I avoid those Christians who separate science and religion because I cannot understand them. Their discussions make no sense to me. Perhaps this is easier for rural Christians to understand than city Christians? I live in a farming area and there is less discussion of any separation when you live closer to the earth. Maybe that is the answer you seek. Get closer to the source of your food. A garden is mentioned in the Bible from time to time. Dig in the dirt from which you came and to which you will return. Plant seeds and watch them grow. Eat the veggies you plant and display the flowers you grow. Then, perhaps, you will understand how wondrous God's creation truly is and will not consider a separation of religion and science. I pity those who cannot see that science and Christianity are not separate but joined through their creator, God.