After the study of weather, weather elements and weather maps. It is really important for the students of geography to attain knowledge about the instruments used for the study of weather. Following are the instruments that are used for the study of weather: 1. Six’s Maximum and Minimum Thermometer 2. Aneroid Barometer 3. Wind Vane 4. Animometer 5. Wet and Dry Bulb Thermometer 6. Rain Gauge.
Instrument # 1. Six’s Maximum and Minimum Thermometer:
Temperature of wind is one of the most important aspects in the study of weather. Commonly to measure the temperature a narrow tube of glass is used which have alcohol or mercury in it. A scale is printed on tube which is divided into 0° to 100°c. This scale shows boiling to freezing points temperature of water In India, degree Celsius/centigrade scale is used. In some countries Fahrenheit scale is also used. In Fahrenheit scale, boiling point is 212° and freezing point is 32°.
These two scales may be converted in one another according to the following methods:
C = 5/9 (F – 32) or F = 9/5 (C + 32)
Figures & statistics of daily temperature are required for weather maps. For this we use a special thermometer and we do not have to check it again and again. After setting it once when we check it after 24 hours then we will get information about the maximum and minimum temperature of last day. This thermometer has narrow ‘U’ shape tube and has bulbs on its both ends.
The bulb on left side is completely filled with Alcohol while bulb on right side is partially filled with Alcohol and ‘U’ shaped tube is filled with mercury. Two iron pins (Pieces of thin wire having size about 1 cm) are placed above mercury on both sides. These pins move on their place due to the up and down movement of mercury.
Movement of mercury has been controlled by the left bulb completely filled with alcohol. As the temperature rises, the Alcohol expands which results in the downward movement of mercury in the left tube and upward movement in right side tube because of this iron pin moves upward in the right side tube.
On the other hand viscosity/density of alcohol is less than the iron pin in the left tube because of which mercury moves down without making any change in the position of iron pin in right tube represents the highest temperature.
As the temperature starts decreasing, the alcohol in the bulb of left tube starts shrinking and because of this mercury starts retreating. To be more specific, mercury retreats in right funnel while rising in left funnel.
If temperature goes on decreasing, the iron wire gets rising in left funnel with the help of rising mercury. This process continues till temperature does not reach at lowest ebb. Finally lower end of iron wire shows minimum temperature.
It is mentionable here that temperature scale decreases as we go higher in left funnel whereas the scale increases upwards in right funnel. This helps in narrating minimum and maximum temperature through the thermometer. To set the thermometer we have to set pieces of iron wire daily with the help of magnet. Iron wires need to touch the mercury in both the funnels.
For this purpose small magnet is used. This activity should not be carried out at highest or lowest temperature, evening time is best for this processing so that on next morning we can record the lowest temperature of night and in the evening we can record the highest temperature of the day recorded in the afternoon.
With the help of these figures we can find out daily mean temperature, daily mean temperature difference. Monthly mean temperature, Annual temperature difference and daily normal temperature.
Instrument # 2. Aneroid Barometer:
Air pressure is an important aspect of air. Like all physical items, air also contains weight. Air pressure of a particular place changes within a short span of time and it also varies from place to place. Information of every second of Air pressure is necessary for the intimation about rain, winds, storm, clear weather etc.
This information is important for pilots and fisher’s Aneroid barometer has been used to measure the air pressure. Air forces Navy and Mountaineers use this to measure the pressure and also to find out the height from the sea level. Liquids are not used in this device/it is a small round metal box in which vacuum is created.
With the increase in air pressure the cap of box moves down and it rises with the decrease in pressure. Although the change in air pressure brings a little change in the cap but it has been multiplied with the help of levers.
These levers are connected with a needle, so that the change in pressure can be recorded on the scale of dial made on the box and it can be measure in centimeter, Inches and Millibars. Inspite of these units sometimes words like storm, rain, clear, dry etc. are also printed on scale so that a person who is not aware about the details of air pressure, can also acquire information about air pressure.
It is also important to mention that to record the change in air pressure on timely basis a red colour needle is fixed on the glass cap of the device. Needle fixed above is set in the direction air pressure needle is with the change in air pressure, pressure needle changes its position and change may be noted accordingly.
Instrument # 3. Wind Vane:
Wind is another aspect of weather, as we know that winds move from high pressure to low pressure areas. Direction and speed of winds is very important in the study of weather. A simple instrument has been used to find out the direction of winds and it can be easily made. A light weight metal piece has been used in it and it might be in the shape of ‘arrow’ or ‘cock’. Its one end is narrow and other is wide.
This metal piece is connected with a iron rod in such a way that it can easily rotate. When wind blows the narrow part of metal piece point towards that direction from which wind is blowing towards this device.
Four iron connected diagonally to one another and pointing towards four directions namely North, South, East and West are fixed beneath this instrument.
Commonly these devices are installed 10 meters higher than land so that it may face moving wind freely. These are installed at wide open places and above the enclosed building.
It is really important to mention a fact for the information of students that name given to the winds is related with their direction. E.g. winds coming towards Punjab from east a (Purab) are known as ‘Pura’ and winds coming from west (Passhim) are known as ‘Pasho or Pashwa’. Similarly there are southern and mountainous winds.
Instrument # 4. Animometer:
After direction of winds, other aspect is speed of winds. Speed of winds is measured with the help of Animometer. There are various Animometers with Slight differences but Robinson Cup Animometer is used the most. It is made of three or four metaled hemispherical cups installed at the horizontal spokes resting upon vertical spindle. These cups start rotating with even hardly blowing wind and with the help of axle and gear attached beneath. Speed of wind meter per second is noted.
Instrument # 5. Wet and Dry Bulb Thermometer:
As we know wind always have gaseous part of water in it. Amount of vapours vary with time and place. Presence of vapours in wind is directly related with temperature. Gaseous form of water in atmosphere is known as ‘Humidity’.
There are three main measurements of humidity: Absolute, Relative and Specific. Among these three relative humidity is the most used because the prior information about saturation of air plays a vital role in the prediction of rain and relative humidity describes it better than other two types of humidity.
The ratio of water vapours present in air at particular temperature and capability of air to carry humidity is known as absolute humidity. This is measured and represented in percentage.
Dry and wet bulb thermometer is used to measure the absolute humidity. This thermometer has two casual thermometers installed on a wooden board in upright position the bulb of one of the thermometer is wrapped in cloth and another end of that cloth is dipped in water in such a way that bulb of this thermometer remain wet.
This thermometer is known as wet bulb thermometer. The second thermometer is not covered by any cloth and is left open. This is known as dry bulb thermometer. Both the thermometers record different temperature & because temperature of wet bulb is lesser than that of dry bulb because of coolness created by moisture & evaporation.
The difference between the temperatures of these two thermometers is directly related with the moisture present in air, meaning thereby, if moisture is higher, evaporation shall be more and it shall create more cooling effect resulting into greater difference of temperature between two thermometers.
It means that the temperature recorded by wet bulb thermometer is always low as compared to the dry bulb thermometer. A special table (chart) is used to check the atmospheric humidity, which is provided on the purchase of this device. Its sample is given below.
E.g. If the temp. of dry bulb thermometer of a place is 90° F and the temperature of wet bulb thermometer is 82°F and their difference is 8°F. Now to calculate the absolute humidity, we refer to the chart in which temperature of dry bulb thermometer being 90°F and difference between two thermometers being 8°F, humidity shall be 71%.
Commonly absolute humidity has been recorded at 8:30 in the morning and 5:30 in the evening. This device should not be exposed to direct sunlight. For this weather scientists use a special wooden box which protects this device from direct sunlight but wind passes through it freely. This device is installed away from buildings and trees in an open place at the height of 1 meter from the ground. This device is also used for other weather devices also, such as Stevenson screen.
Instrument # 6. Rain Gauge:
Falling of water vapours from air/sky in the form of drizzle, rain, sleet, snow, grapple and ail is known as precipitation. It has been measured in centimeters or inches. When we say that a particular place has received 10 millimeter rainfall then it means that if the water do not move below the surface and it is not converted into vapours due to evaporation and Run off process do not take place then a 10 millimeter high layer of water will be collected at that place.
To measure the rain fall a simple device is used which has two metal cylinders and a funnel. Bigger cylinder has a funnel by same size and its narrower side opens in the cylinder which accumulates rain water.
Funnel is kept 10 centimeter below the big cylinder so that water droplets do not fall out because of any kind of movement.
Smaller cylinder is actually a measurement jar with milimeters, centimeters and inches marked on it. Measurement jar and the funnel have areas with specific ratio. This measurement jar is narrow cylindrical jar so that it may measure even slightest of rain water.
In weather maps of India figures of rainfall are included on the basis of total rainfall during last 24 hours at a particular place. Basically these are recorded at 8 O’clock in the morning.
This device should be used at an open place away from buildings and trees, where rainfall can be recorded freely. It should be kept 1 foot high from the ground so that water droplets after striking the ground do not enter into funnel. It should be placed away from children and animals at a safe place so that we can protect it from falling.
Drawing of Isotherms, Isobars and Isohyets:
There is only one method to draw Isotherms, Isobars and Isohyets or any other kind of isolate lines on maps.
First of all figures about maximum places are required for given map. Larger the number of figures, result has better representation. Second step is to identify the places which have maximum and minimum value of isopleths so that variation value may be finalized. Third and last step is to draw isopleths which is to be begun from lowest value to upper value grades. The isopleth with highest value is to be drawn in the end.
For the facility of students can practice with the figures of local place or other states with the help of their teachers. Prepare isobar and isohyet maps also.