Images Dated 27th August 2004

Ouchi illusion

Ouchi illusion. The central circular area of perpendicularly orientated bars appears to move and float compared to the surrounding pattern. The effect is particularly marked when the observer moves relative to the image. It is thought that the circular contour leads to ambiguity as to where the vertical bars terminate, and hence to ambiguity as to its own position. The brain therefore fails to integrate the whole image into a cohesive whole and so our eye movements cause apparent motion

© SCIENCE PHOTO LIBRARY

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