Before an answer can be given, you need to supply what theory you are talking about. Basic rule of asking a question: always assume the reader can't read your mind or guess what you are asking. The more info you supply, the better the answer will be.
The microscope! :)
No one haha it just was there for like ever
light microscope
The flash light and the ruler and goggles
Other scientists like Lamark Baptist Wallace helped by going out and exploring with him and publishing his articles.
once a hypothesis has been supported in repeated experiments, scientists can begin to develop a theory.
The Microscope.
Light microscope
many differnet scientists doing expiraments that prove the hypothesis to be true-then it becomes a theory
The principle of fossil succession and the theory of evolution have helped scientists explain the fossil record.
Three German scientists. Matthias Schleiden, Theodor Schwann and Rudolph Virchow.
once a hypothesis has been supported in repeated experiments, scientists can begin to develop a theory.