Question

Observations are things that can be perceived with senses (i.e., sight, sound, smell, taste, and touch).

Inferences are decisions based on what was observed.

Use specific examples from Joseph Priestley’s experiment to explain the relationship between what he observed and what he inferred.

Answer 1

Start with the definitions:
- Observation = something you perceive with the senses (what you actually see, hear, smell, etc.).
- Inference = a conclusion you draw from those observations about what is happening or why.

Using Priestley’s work (about 1774) gives clear examples of how observations lead to inferences.

1) Heating mercuric oxide and collecting a gas
- Observation (sight): When Priestley heated mercuric oxide he saw a colorless gas collect in an inverted jar over mercury.
- Inference: A new, distinct kind of “air” had been produced by the heating (i.e., the substance had decomposed and released a component of air).

2) Burning a candle in the collected gas
- Observation (sight): A candle burned much more brightly and vigorously in the collected gas than in ordinary air.
- Inference: That gas must be especially good at supporting combustion — it contained something that enhanced burning more than ordinary air did.

3) Putting a mouse into the collected gas
- Observation (sight): A mouse survived longer in the collected gas than it would in a small volume of ordinary air.
- Inference: The gas was also better at supporting life (respiration) than ordinary air; it had a property necessary for breathing.

4) Plants “restoring” foul air
- Observation (sight): Air that had been “injured” by burning or breathing could be restored by placing a mint plant in it and exposing it to sunlight; after that the air again supported combustion and life.
- Inference: Plants produce or release something into the air that renews its ability to support combustion and respiration.

How inferences can change: Priestley interpreted these inferences in terms of the phlogiston theory then current — he called the gas “dephlogisticated air,” thinking it was air lacking phlogiston. Later, Lavoisier reinterpreted the same observations to conclude the gas was a component of air (oxygen) that combines with substances during combustion and respiration. This shows that the observations (what was seen) remain the same, while the inferred explanation (why it happens) can change as theories and additional evidence evolve.

Summary: Priestley’s observations (colorless gas, brighter flame, longer-living mouse, plants restoring air) were empirical sensory data; his inferences were the conclusions he drew about the gas’s role in combustion and respiration. Observations provide the facts; inferences are the scientific explanations built from those facts and subject to revision.