  During that period philosophers turned much of their attention to the study of the logical structure of scientific theories and its connection to evidence. The tenets of logical positivism influenced this area of investigation — as well as philosophy more generally — at the time. One of these tenets stated that observational and theoretical propositions in science are separable. My readings of the gradation on the scale of a mercury thermometer can be separated from rather complicated theoretical statements concerning heat transfer and the theoretical concept of temperature.