Images Dated 27th August 2004

Mercury thermometer

Mercury thermometer showing a room temperature of 24 degrees Celsius. The mercury thermometer works as mercury, a liquid metal, expands evenly as the temperature increases. As it expands it fills more and more of a narrow tube, which is marked with a scale in degrees

© ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY

24 Degrees Celsius, Device, Equipment, Measurement, Measuring, Mercury, Physics, Room Temperature, Single, Thermometer

Simultaneous contrast

Simultaneous contrast example. The green squares look brighter on the left, where they are in yellow bands, compared to the right, where they are in blue bands. There is no actual difference between them. This is a demonstration of the effect known as simultaneous contrast - the phenomenon whereby the perception of different colours is altered by their surroundings. There has been some debate - most notably amongst the 19th century scientists Helmholtz and Hering - as to whether this results from neurological effects or from retinal pre-processing. It is likely that it is a combination of the two

© SCIENCE PHOTO LIBRARY

pH measurement of oxide solutions

pHs of oxide solutions. Aqueous solutions of the oxides of some elements with universal indicator (UI) added to show their pH (acidity). The element forming each oxide is labelled. The oxide of sulphur produces sulphuric acid, which has the lowest pH (strongest acidity). UI changes colour according to the pH, from red (most acidic) through yellow (mildly acidic) to blue (slightly alkaline) to purple (strongly alkaline). Sulphur oxide forms sulphuric acid in water, which is highly acidic. Sodium oxide forms sodium hydroxide (a strong alakai). Oxide pH increases from left to right across the periodic table

© ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY