hes@ecsvax.UUCP (Henry Schaffer) (10/26/85)
> When an ordinary mercury thermometer at room temperature is inserted > into a beaker of boiling water, the mercury actually descends a > small but noticeable amount before ascending to the 100 C level. > Why? > > Steve Harris Before the mercury can expand because of the heat, the glass surrounding the mercury must get hot to pass on the heat. The glass does expand somewhat *before* the mercury heats up. This expansion increases the volume of the "container" holding the mercury, and so the mercury will descend. For a small (rate of) change in the temperature the effect should be very small, but room temp. to boiling water is not a small change. --henry schaffer