Text b. Secular variations of geomagnetic field

I. Read aloud and memorize the following words;

allow - дозволяти, робити можливий, допускати

core - ядро

datum - data – дане, дані

determine - визначати

distinctly - чітко, ясно

distinguished - відмінний

embrace (v) - охоплювати

focus - центр

geodynamic - геодинамічний

investigate - розслідувати

ionosphere - іоносфера

lithosphere - літосфера

magnetosphere - магнітосфера

period - період

physico-chemical - фізично-хімічний

reflect - відображати

regional - регіональний

seismoprognostic – сейсмопрогнозний

so-called - так званий

territory - територія

variability - мінливість, непостійність

II. Expressions for the text comprehension

as a rule - як правило

complicated spectrum - складний спектр

different depths - різні глибини

different sources - різні джерела

earth's crust - земна кора

existing chain - існуючий ланцюг

geodynamic processes - геодинамічні процеси

geodynamic variations - геодинамічні зміни

geomagnetic field - геомагнітне поле

global peculiarities - глобальні особливості

in general - взагалі

local anomalies - місцеві аномалії

local component - місцевий компонент, складова

local effects - місцеві впливи

magnetic observatory - магнітна обсерваторія

physico-chemical phenomena - фізико-хімічні явища

secular variation – вікова зміна

spatial structure - просторова структура

surface layer - поверхневий шар

tectomagnetic effects - тектомагнітні впливи

testing ground – полігон

upper mantle - земна мантія

wide range - широкий діапазон

Secular variations of geomagnetic field

Variability of geomagnetic field in time and in a wide range of periods - from minutes to hundreds and thousands of years reflects a complicated spectrum of physico-chemical phenomena in the core, lithosphere, ionosphere and magnetоsphere of the earth, to investigate modern geodynamic processes at different depths, from the surface layers of the earth's crust to the core of the earth, data on geomagnetic variations with the periods over 1 year, the so-called secular variations (SV), are widely used. In general, geomagnetic field variations can be considered as a vector sum of the fields from different sources. In the spatial structure of secular variations of geomagnetic field there are distinctly distinguished global, regional and local components. Global peculiarities or focuses of SV embrace areas of thousands of kilometers and have their sources in the earth's core. Regional and local effects are determined by modern physico-chemical, geodynamic and electromagnetic phenomena in the earth's crust and upper mantle.

The existing chain of magnetic observatories on the territory of Europe allows to study in details the global and regional effects in SV. The local anomalies of SV or the so-called tectomagnetic effects ere studied, as a rule, in geodynamic and seismoprognostic testing grounds.

A s s i g n m e n t s

I. Comprehension questions:

1.How does geomagnetic field vary? 2. What are secular variations? 3. At what depths are geodynamic processes studied? 4. What іs distinguished in the spatial structure of secular variations? 5. Where are local anomalies of SV studied? 6.What territory do SV embrace?

2. Speak on sources of geomagnetic variations.

Lesson 7.

Text A. The plane table

1.Read and memorize the following words:

acre – акр

alidade - алідада

base (n) - база

board (n) – дошка

carefully - дбайливо, уважно

clamp (v) – скріпляти

connect - зв’язувати

construct – будувати

dependent – залежний

device - прилад, пристрій

directly – безпосередньо

distortion – перекручення

economical - економічиий

edge - край

flat (a) - плоский

graphically - наочно, графічно

ground (n) – земля, грунт

however – проте

limit (v) -обмежувати

map (v) – картографувати

moisture – волога

move (v) - рухатись

obtainable - доступний

orient (v) – орієнтувати

party – партія

plot (v) - креслити, зображувати

practicable – практичний

precision – точність

preserve (v) –зберігати

protect – захищати

prove – виявитись

rapidly –швидко

reliable – надійний

require - вимагати

result - peзультат

rise (v) - підніматись

run (v) - використовувати заповнювати

run out – використовувати

sketch (v)- накреслювати

sketching (n) - ескіз

straight - прямий

support (v) - підтримувати

top (n) - верх

topographer – топограф

tripod – тринога

II. Expressions for the text comprehension:

accuracy of points - точність точок

as small as - не більше

aсcurасу of plot - точність зображення

burden the memory - обтяжувати пам’ять

contour interval - контурний інтервал

desired azimuth - бажаний азімут

drafting board - креслярська дошка

elaborate notes - детальні замітки, нотатки

elevation of triangulation - висота трiангуляції

favourable weather - сприятлива погода

field work - польова робота

for instance – наприклад

for this reason - з цієї причини

horizontal axis – горизонтальна вісь

important advantage - важлива перевага

located points – знайдені точки

metal column - металева колона

office work - камеральна робота

on a small scale - в малому масштабі

open country - відкрита місцевість

piece of metal - шматок металу

plane of telescope - площина труби

plane table - мензулa

plane table survey - зйомка за допомогою мензули

proper position - відповідне положення

pег day - в день

stadia hairs - горизонтальні паралельні нитки

system of triangulation - система трiангуляції

tape traverse - тригонометричний хід стрічки

topographic method - топографічний метод

topographical map - топографічна карта

transit and stadia method - метод тахіометрії і теодоліту

traverse points - точки тригонометричного ходу

usual size - звичайний розмір

vertical arc - вертикальна дуга

vertical mоtіоn - вертикальний рух

The plane table

The plane table is used for constructing a map directly in the field. The paper is fastened to a board, like a drafting board, supported on a tripod with a device for levelling and clamping so that it can be oriented in any desired azimuth. The usual size of the table is 24 by 30 inc. On the map alidade is used to define directions and measure distances. It has a telescope equipped with stadia hairs and is mounted on a horizontal axis resting in Y supports. These are connected to a metal column which rises from the centre of a flat piece of metal about 18 in. long of which both edges are straight and parallel to the plane of the telescope. On this base are two spirit-levels for levelling the table. The telescope has only a vertical motion and a vertical arc. The entire alidade is moved about on the top of the map after the table has been levelled.

The use of the plane table has generally been limited to topographical maps drawn on a small scale. A system of triangulation or a transit and tape traverse may first be carefully surveyed and plotted on a map. Levels also may be run to determine the elevation of triangulation or traverse points which will then be used as a control for plane table survey. In this case the plane table is used only to fill in details and accurate maps on a scale as small as 40 ft. to the inch can be rapidly made.

The most important advantage of the plane table over other topographic methods is that all the sketching is done in the field where topographer can see the form of the ground that be is mapping. He can sketch details at once in their proper position without burdening his memory and without making elaborate notes, for this reason details may be accurately sketched from much smaller number of located points than would be required, for instance, by the transit and the stadia method.

If not practicable to run out system of triangulation or a transit and tape traverse the plane table can be used for making such a survey graphically. In all cases, however, the accuracy of these points located by the plane table is limited by precision of the plotting rather than of the measurements. In the field the map must be protected from distortion by moisture so as to preserve accuracy of the plot. Celluloid sheets are obtainable which can be used even in rainy weather.

The plane table method usually requires more time for field work than the transit and stadia methods. It is also more dependent upon favourable weather. But taking into account both the field and the office work the plane table has proved more economical than the transit and stadia for the work in open country and the results are more reliable. In open country a contour interval of 5 ft. being required, a party of 3 men should survey about 8 acres per day.

E x e r c i s e s

I. Give Ukrainian equivalents of the following international words from the text;

construct, orient, azimuth, alidade, distance, horizontal, metal, column, centre, parallel, base, telescope, vertical, topographical, system of triangulation, control, detail, scale, topographer, form, position, method, practicable, graphically, celluloid, resuilt,contour interval, party,acre.

I1. Wordbuilding:

a) give all possible derivatives: to construct, to direct, to define, to measure, to connect, to limit, to determine, to fill, moist, to preserve, plot, to obtain, to require, graph, to form

b) form adverbs from adjectives and translate them: rapid, direct, usual, definite, vertical, horizontal

I11. Learn synonyms:

motion - movement, entire - full - whole, a map - a chart, to raise -- to lift, control - check, a transit - a theodolite, accuracy - precision, for instance - for example, to take into account - to take into consideration, elaborate – complicated

IV. Read the text again, write out sentences with ing-forms, define their functions and translate them into Ukrainian

V. Finish the sentences according to the text:

1. The plane table is used for constructing ….. 2. Alidade is used to define ….. 3.The telescope has a vertical motion and ….. 4. In the field the map the map must be protected ….. 5. A party of 3 men should survey …

VI. Comprehension questions:

1.When is the plane table used? 2. Can the plane table be oriented in any desired azimuth? 3. What is the usual size of the plane table? 4. What is alidade used for? 5. Where is alidade mounted? 6. How many spirit levels are there on the plane table? 7. What kind of motion has the telescope? 8. What is used to control the plane table survey? 9. What is the advantage of the plane table? 10. Is the accuracy of the plane table measurements limited? I1. What contour interval is required in open country surveying?

VII. Say what conclusion could be drawn from the fact that the use of the plane table is limited to small-scale topographical maps.

V1II. Speak about:

a) the plane table arrangement ;

b) the plane table use;

c) the plane table advantages;

d) the plane table disadvantages

Text B. Trigonometric levelling

I. Read aloud and memorize the following words;

average(v) – виводити середнє число

coefficient - коефіцієнт

combine (v) – поєднувати(сь)

consist in – полягати в

eliminate - ліквідувати

erect (v) – підніматись, встановлювати

height - висота

instrument - інструмент

locality - місцевість

record (v) - реєструвати

signal (n) - сигнал

station - станція

uncertainty - невпевненість

vary - змінюватись

II. Expressions for the text comprehension:

atmospheric pressure - атмосферний тиск

chief difficulty - головна трудність

compute the difference - обчислити різницю

horizontal angle - горизонтальний кут

horizontal distance - горизонтальна відстань

independent reading - незалежний показник

on the basis of - на основі

ordinary theodolite - звичайний теодоліт

refraction of air -рефракція повітря

simultaneous observations - одночасні спостереження

single reading - одиночний показник

special vertical circle - спеціальне вертикальне коло

telescope direct - труба з прямим зображенням

telescope inverted - труба теодоліту з зворотнім зображенням

the only way - єдиний шлях

triangulation work - тріангуляційна робота

trigonometric levelling - тригонометричне нівелювання

vertical angle - вертикальний кут

Trigonometric levelling

Trigonometric levelling consists in computing the difference in elevation of two points on the basis of horizontal distance and the vertical angle between them. It is usually combined with the triangulation work, the vertical angles being measured at the same time as the horizontal angles, a vertical angle is measured to some definite point on the signal the height of which above the station was determined when the signal was erected. The height of the instrument above its own station should also be measured and recorded. In a very precise work angles are measured with a special vertical circle instrument. In a less precise work an ordinary theodolite the vertical arc of which reads to 50 sec. or to 20 sec. may be used but with such instruments only single readings can be made. In this case the best results are obtained by averaging several independent readings half of which are taken with the telescope direct and other half with the telescope inverted.

The chief difficulty in obtaining accurate results by trigonometric levelling is the uncertainty in the coefficient of refraction of the air. This varies with locality, temperature and atmospheric pressure and the only way its effect can be eliminated is by taking simultaneous observations between two stations.

A s s i g n m e n t s

I. Comprehension questions;

1.What does trigonometric levelling consist in? 2. With what is trigonometric levelling combined? 3. When are vertical angles measured in trigonometric levelling? 4. How are angles measured in a very precise work? 5. What is the disadvantage of a less precise work in trigonometric levelling? 6. How does the coefficient of air refraction vary? 7. What telescopes are used in trigonometric levelling?

2. Speak on the procedure of trigonometric levelling.