An example of an historical idea which would now be considered an alternative conception:
"Somebody suggested that the phlogiston might have negative weight, a positive virtue of 'levity', so that a body actually became heavier after losing it. Such an hypothesis, however, made a serious inroad on the whole doctrine of a solid phlogiston; and we can see that this ancient idea of 'levity' had ceased to be capable of carrying much conviction by the eighteenth century. …. The more popular view seems to have been that while the burning produced a loss of phlogiston and a loss of weight, a secondary and somewhat incidental operation occurred, which more than cancelled the loss of weight.
…it was possible to hold the phlogiston theory and still believe that weight was gained in combustion as a result of something which was taken incidentally from the air this on a sufficient scale to override any reduction that had been produced by the loss of the phlogiston."
Herbert Butterfield (1957) The Origins of Modern Science 1300-1800 (New Edition: Revised and enlarged). G. Bell and Sons Ltd., London.
