During the 20th century musicians started to realize that the way we play the music of Bach and other composers was making the music sound different from how it would have been first heard. People became interested in hearing what the music would have sounded like back in the 17th and early 18th centuries (the Baroque period). Few of the old instruments still existed and many that had survived had been “modernized”. So instrument makers started to make instruments in the old ways. Some musicians and orchestras started to play these instruments. The instruments are often called “period instruments” (or "authentic instruments" or "historical instruments") because they are made so that they are like instruments of earlier periods.
Today's instruments of the string family (violin, viola, cello and double bass) may look almost the same as the old ones, but there are differences: the old fingerboards were shorter and the strings used to be made of gut, not metal. The bows were shaped differently, and the technique of playing was also different.
Woodwind instruments have changed a lot since the old times. Flutes, oboes and bassoons hardly had any keys (the metal keys which help to cover the holes). The keys were added in the 18th century and it made it much easier to play difficult music with lots of sharps and flats. Clarinets were not invented until the late 18th century, but even they have developed a lot since Mozart’s time (1756-1791).
Brass instruments like the trumpet and French horn now have valves which make it easier to play in different keys. The trombone is the only instrument which has not changed. The tuba was invented in the early 19th century.
Percussion instruments include the timpani which have changed a lot. In Baroque times they had calf-skin heads but now the heads are made of plastic. This makes a very different sound.
Baroque keyboard instruments included the harpsichord and clavichord. The piano was invented during the 18th century. It still sounded very different when Mozart wrote for it. The frame was made of wood, not of cast iron, and the hammers had leather heads instead of felt. A modern piano sounds quite different.
The interest in period instruments started in the mid 20th century. People like Wanda Landowska played Baroque keyboard music on the harpsichord instead of the piano. Conductors like Nikolas Harnoncourt have trained small orchestras to play on period instruments using techniques which were used in Baroque times. Gradually musicians also started using period instruments for music from the Classical music period (the time of Mozart and Beethoven). Even in the mid 18th century the modern orchestra had not yet evolved. In recent years conductors like John Elliot Gardiner have performed music by Hector Berlioz on period instruments. There are now many small instrumental groups and orchestras who regularly perform on period instruments e.g. The English Concert and the English Baroque Soloists.
Does old music sound better on period instruments? Musicians do not all agree about this question and they still argue a lot about the way that some of the music should be played. However, it is important to listen to the way that period instruments are played. Musicians such as the violinist Andrew Manze have done a lot of research in old books and old music and have done a lot to make people rethink the way in which music from former centuries should be performed.
Monogenea
Monogenea are a type of flatworm. They are parasites which means that they always need another creature to live on. They live on the outside of their host. Some parasites, like tapeworms, live on the inside of a larger creature.
Monogenea are especially common on the skin, fins and gills of fish. Less commonly, they can be found in the urinary bladder and rectum of cold-blooded vertebrates. No types of Monogenea infect birds, but one ("Oculotrema hippopotami") infects mammals. It is a parasite in the eye of a hippopotamus.
Monogenea are usually hermaphrodites. This means that they have both sexes. First they are males, and only later do they become females as well. They have direct life-cycles with no asexual reproduction (unlike the Digenea). In those types of Monogenea that lay eggs, the young ones grow to a larval stage called an "oncomiracidium". It is at the "larva" stage that they are able to travel from one host creature to another. When they are adults, Monogenea eat the blood, mucus, and epithelial cells of their host creature.
Turbellaria
Turbellaria are a class of free-living flatworms. Most of them are carnivores. They actively search for food. Most of them are small, less than 60 cm in size. Almost all of them are aquatic. Some also live on land, in damp places.
Bifröst
In Norse mythology, Bifröst is the bridge between the land of mortals, Midgard, and the land of the gods, Asgard. The gods cross it every day to meet and decide things at Urdarbrunn (Well of Urd) under the tree Yggdrasill. The bridge is a rainbow. It was built by the Æsir and is guarded by the god Heimdall.
Only the thunder god Thor was not allowed to use the rainbow, because he may break it. The bridge will be destroyed at the end of the world, Ragnarök, when the relentless army of giants and the dead run on it to attack Asgard.
Alternative names: Bilröst, Ásbrú, Bifrost.
Mendoza Province
Mendoza is a Province of Argentina. It is in the region called Cuyo. The province borders San Juan in the north, San Luis and La Pampa in the east, Neuquén in the south, and Chile to the west.
It is the major wine producer of Argentina and has many other crops. It has the highest mountain in the country, Aconcagua.
Mendoza has a population of 1,579,651 people (2001). Spanish is the main language but many people also speak English, Italian and Portuguese.
Dosimeter
A dosimeter is a tool that can measure different levels of hazardous environments. Common dosimeters are those used for sound (They measure how loud a certain noise is) and radiation (they measure how much radiation there is in an environment).
Geiger counter
A Geiger counter (sometimes called Geiger-Müller counter) is an instrument that measures ionizing radiation such as alpha particles, beta particles, or gamma rays. It is best known as a hand held radiation survey instrument, but it can also be used as a bench instrument or permanently installed.
The original operating principle was discovered in 1908 and since the subsequent development of the Geiger-Müller tube in 1928 the counter has been a very popular instrument due to its robust sensing detector and element and relatively low cost.
The radiation sensor is a Geiger-Müller tube which gives out an electronic signal when radiation is present.
The readout is counts or radiation dose. The counts display is commonly "counts per second". Radiation dose rate is displayed in a unit such as the sievert.
The readout can be analogue or digital, and modern instruments have communications with a computer or network.
There is usually an option to produce audible representing the radiation intensity. This allows the user to concentrate on manipulation of the instrument without looking at the display.
For alpha particles and low energy beta particles the "end window" type of GM tube is used as these particles have a limited range even in free air and are easily stopped by a solid material.
Geiger counters can be used to detect gamma radiation, and for this the windowless tube is used. A special type of the Geiger tube is used to measure neutrons.
For hand-held units there are two fundamental physical configurations: the "integral" unit, with both detector and electronics in the same unit, and the "two-piece" design which has a separate detector probe and an electronics module connected by a short cable.