Archive for August 1st, 2010

August 1, 2010

Shepard Tone

penrose stairs

A Shepard tone, named after Roger Shepard, is a sound consisting of a superposition of sine waves separated by octaves.  This creates the auditory illusion of a tone that continually ascends or descends in pitch, yet which ultimately seems to get no higher or lower.

August 1, 2010

Penrose Stairs


The Penrose stairs is an impossible object created by Lionel Penrose and his son Roger Penrose. It can be seen as a variation on the Penrose triangle. It is a two-dimensional depiction of a staircase in which the stairs make four 90-degree turns as they ascend or descend yet form a continuous loop, so that a person could climb them forever and never get any higher. This is clearly impossible in three dimensions; the two-dimensional figure achieves this paradox by distorting perspective.

The best known example of Penrose stairs appears in the lithograph Ascending and Descending by M. C. Escher, where it is incorporated into a monastery where several monks ascend and descend the endless staircase. The staircase had also been discovered previously by the Swedish artist Oscar Reutersvärd, but neither Penrose nor Escher were aware of his designs.

August 1, 2010

Salty Liquorice

salmiak skull

Salty liquorice, salmiak or salmiakki is a variety of liquorice that contains a relatively large amount of ammonium chloride (salmiac) in addition to the liquorice root extract, sugar, and starch or gum arabic that constitute normal liquorice. Ammonium chloride has a spicy taste that vaguely resembles that of sodium chloride (table salt). However, salty liquorice does not necessarily contain any sodium.

Although some types of regular liquorice can also contain a small amount of ammonium chloride, salty liquorice can contain up to about 8 percent of ammonium chloride. Moreover, the salty taste is typically less masked by a high sugar content compared to regular liquorice. Salty liquorice candies are almost always black or very dark brown and can range from very soft to very hard and may be brittle. The other colors used are white and variants of grey.