What does "measurement" mean in the given context?

Question

Although not the explicit goal, the best science can really be seen as refining ignorance. Scientists, especially young ones, can get too obsessed with results. Society helps them along in this mad chase. Big discoveries are covered in the press, show up on the university’s home page, help get grants, and make the case for promotions. But it’s wrong. Great scientists, the pioneers that we admire, are not concerned with results but with the next questions. The highly respected physicist Enrico Fermi told his students that an experiment that successfully proves a hypothesis is a measurement; one that doesn’t is a discovery. A discovery, an uncovering ― of new ignorance. The Nobel Prize, the pinnacle of scientific accomplishment, is awarded, not for a lifetime of scientific achievement, but for a single discovery, a result. Even the Nobel committee realizes in some way that this is not really in the scientific spirit, and their award citations commonly honor the discovery for having "opened a field up," “transformed a field,” or “taken a field in new and unexpected directions.”

Source: Ignorance: How It Drives Science By Stuart Firestein · 2012

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Does "a measurement" mean "the act of measuring" or does it mean "extent, size, etc., ascertained by measuring."?

Answer 1

Measurement means "finding the value of some physical quantity".

He is speaking rhetorically. A measurement is not an exciting thing to a scientist. Fermi is using this word to persuade us that an experiment that confirms a hypothesis is not an interesting result. It is at best assigning a more accurate value to something that we already believe.

On the other hand, an experiment that contradicts a hypothesis changes what we believe.

Example: Many scientists have the hypothesis that there are particles of dark matter. Confirming this hypothesis would involve measuring the mass of these particles. That would be less exciting than discovering that these particles don't exist, and so the theories of cosmology have to be re-written.

Answer 2

The author mentions how Fermi said that "an experiment that successfully proves a hypothesis" is—merely—an act of measuring.

Fermi was trying to show his students that it's not the obvious hypothesis, not the confirmation of probability that drives science, but the discovery of what we don't know.

Answer 3

James's answer is very good for explaining what was meant by Fermi in the paragraph. Fermi is not literally speaking about what a measurement is.

The poster also asked this question which happens to be a bit separate from the Fermi question, as Fermi wasn't really 100% serious:

Does "a measurement" mean "the act of measuring" or does it mean "extent, size, etc., ascertained by measuring."?

Measurement both refers to an "act of measuring" and the value ascertained by measuring. Fermi refers more to the latter, because he is talking about results.

When you say "I take a measurement," you are referring to the former. When you say "What is that measurement?," you are referring to the latter. When you say "how many measurements?" someone may either answer the total number of acts of measurements that they took, or the total number of final values, depending on the context.