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2.6 Turning the handle

The owners of the original hand-cranked gramophones were instructed that the standard velocity for ‘seven-inch plates’ was about 70 revolutions per minute. The owner was also warned that failure to turn the plate at the correct speed would lead to a lowering of the pitch if turned too slow, or a raising of the pitch if turned too fast. It is doubtful if true reproduction of the recorded sound was ever achieved by the owners of these machines! A better power source was needed and as electr
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2.1 Edison starts with cylinders

I had a little gramophone; I'd wind it round and round, and with a sharpish needle it made a cheerful sound.

Flanders, M. and Swann, D. (1977) ‘The Song of Reproduction’ from The Songs of Michael Flanders and Donald Swann, London, Elm Tree Books and St George's Press, p. 99

In 1877 the young American inventor Thomas Alva Edison finally completed development of an invention capable of ca
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6.1 Defining amplitude

Another important property of a sine wave we need to be able to specify is its amplitude. In essence, the amplitude of a sine wave is its size. Unfortunately there are various ways of defining what is meant by the size of a sine wave, and you are likely to come across many of them in material you look at outside this unit. Before I explain what our definition is, it will help matters if we look at what is meant by the average value of a sine wave.

Figure 16 shows a sinusoidally a
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12.2 Technology push

The technology push model is a simple linear model that suggests that the innovation process starts with an idea or a discovery – it is sometimes called ‘idea push’ (Figure 51). Sometimes this is by a creative individual who has the knowledge and imaginatio
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3.5.5 Biological indicators

A great many biological species and individuals occur in normal streams. These often differ markedly in their sensitivity to environmental factors, and likewise the tolerances of various species to different types of pollution vary considerably. The major groups of organisms that have been used as indicators of environmental pollution include bacteria, fungi, protozoa, algae, higher plants, macroinvertebrates and fish. The benthic ‘bottom living’ macroinvertebrates are particularly suitab
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3.3.1 Turbidity, colour and suspended solids

As water runs off the land, there are some substances which do not dissolve but are taken along as suspended solids. Then, depending on their sizes and the velocity of the river, the solid particles may settle out at a certain point or be carried on further. Quantities are affected by seasonal changes and tend to be higher in winter because of increased storm runoff due to higher rainfall and melting snow.

The quantity of suspended solids (measured in g m<
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3.3 Physical characteristics of natural waters

A river's physical characteristics include:

  • clarity/turbidity

  • colour

  • speed of flow/turbulence

  • odour

  • the presence of plants and macroscopic animal life.

The physical characteristics are determined by location, geology and climate of the catchment area. In turn they influence the chemical and biological characteristics of the watercourse.

The physical appearance m
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3.1 Water, the medium of life

The list of necessities for the provision of life includes various nutrients and water: water is one of the basic resources needed for the process of photosynthesis. Since it is an excellent solvent, water, even in its ‘natural’ state, is never pure H2O but contains a variety of soluble inorganic and organic compounds. Water can also carry large amounts of insoluble material in suspension. The amounts and types of impurities vary with location and time of year, and determine so
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2.11 Storage

In a given fixed space at any phase of the hydrological cycle, there is an inflow and an outflow of water, the rates of which vary with time. The total cumulative difference between inflow and outflow is the storage. So within that space there is a body of water whose mass is not directly controlled by instantaneous values of inflow and outflow. For example, in river flow the movement of the whole body of water in the channel is generally downstream, yet a given reach contains a volume whose
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2.10 Aquifers

Groundwater is water that, after infiltrating and percolating through surface soils, flows into an aquifer, an underground water-bearing layer of porous rock. About one-third of the UK's drinking water is drawn from aquifers.

To permit economic development, an aquifer must be able to transmit large quantities of water from one point to another and therefore it must have a high permeability. The groundwater contained in aquifers is released from springs an
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2.9 Percolation

Movement of infiltrated water downwards through the zone of aeration (Figure 5) is known as percolation. The infiltrated water which does not remain held by capillary forces in the surface soils moves by the action of gravity through the unsaturated layers of soil or rock until it arrives at the water table. Here the percolated water joins the body of groundwater which seeps slowly to the sea.

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2.6 Precipitation

Precipitation is defined as the depth of rainfall, or the water equivalent of snow, sleet and hail falling during a given measurement period. It may be in the form of rain, snow, sleet or hail, or in minor forms such as dew and hoar frost, but existing theories do not yet satisfactorily account for all the observed characteristics. In tropical climates, precipitation occurs as a result of the gradual coalescence of the tiny condensed droplets as they collide within the cloud
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2.4 Condensation

As air rises it expands, owing to the decrease in pressure with height, and as it expands, in theory it cools at an average rate of 1°C for every 100 m of altitude. As the air cools, it becomes saturated with water vapour which condenses around small particles in the air. These particles may occur naturally, such as soil particles or salt particles residual to evaporation of sea spray, or they may be produced artificially during combustion. A measure of the necessary cooling to produce conde
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2.3 Transpiration

If there were no vegetation, the rate of evaporation from land surfaces after rain would diminish rapidly to a very low value. Plants increase this rate by transpiration. In this process, water is transferred from the soil through the roots to the leaves by osmosis and capillary action. Water evaporates from the surface of the leaves and the resulting vapour diffuses into the atmosphere. For hydrological measurements, this phenomenon is frequently lumped with evaporation because the two proce
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2.1 Introduction

The hydrological cycle, the continuous cycling of water between land, open water surfaces and the sea, either directly or indirectly, is an extremely complex process which has been known for a long time (Figure 1). The identifiable mechanisms of the cycle are complicated not only by the characteristics of air-water-land interfaces across which the cycle operates, but also by climatic factors which vary in both time and space. The various operations and mechanisms within the cycle are illustra
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1 Some facts about water

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