Final answer:
Nigel Spirey's discoveries are not mentioned or referenced in the given information.
Step-by-step explanation:
According to the provided information, Nigel Spirey did not make any specific discovery. The text mentions the discoveries made by astronomers like Vesto M. Slipher and Edwin Hubble regarding the expansion of the universe and the nature of spiral nebulae. Nigel Spirey's discoveries are not mentioned or referenced in the given text.