phlogiston had weight

An example of a historical scientific idea now considered an alternative conception:

"The experimenter [Henry Cavendish] now brought a lighted taper to his six samples of gas. He watched each specimen of gas burn with the same pale blue flame. Strange that the same gas should be evolved in each easel What else could this inflammable air be, but that elusive phlogiston? For had not Becher taught that metals were compounds of phlogiston and some peculiar earths? Surely Cavendish had proved that the gas came, not from the acids or water in the bottles, but from the metals themselves! But he must not announce this until he had investigated further-it would not do to startle the world before he had made certain he was right.

With the crude instruments at his disposal, he passed the gases through drying tubes to free them of all moisture, and then he weighed the pure imprisoned 'phlogiston'. Though extremely light he found it actually had weight. It was ponderable. He had nailed phlogiston itself! Now, at the age of thirty-five, he published an account of this work on Factitious Airs in the Transactions of the Royal Society.

Priestley, accepting these results, discussed them with the members of the Lunar Society and the 'Lunatics', as they were called, agreed with him. [Matthew] Boulton especially was enthusiastic, 'We have long talked of phlogiston', he declared, 'without knowing what we talked about, but now that Dr. Priestley brought the matter to light we can pour that element out of one vessel into another. This Goddess of levity can be measured and weighed like other matter'."

Bernard Jaffe (1934) Crucibles. The Lives and Achievements of the Great Chemists. Jarrolds Publishers.

Phlogiston was considered a substance released on burning.

Referring to phlogiston as the 'Goddess of levity' was to use a metaphor.