Theory:

To understand the ministerial, socio-economic, and civilization advancement in the country’s ancestry, history of modern India assists us. From the beginning of the European invasion all forms of their official communications were recorded and safeguarded. These well-preserved records kept in Europe and India reveals us the connection between India and Europe.
Kinds of Sources
The sources which help us to reconstruct the past can be classified into:
  • Written sources
  • Material sources
Written sources
Written sources are the one which are in the form of written text. It includes contemporary letters, administrative texts, biographies, autobiographies, official documents, political declarations, manuscripts etc. 
India’s wealth abundance is attracted by the Europeans which is known to them by the travellers like Marco Polo, Vasco da gamma and many others.  So they began to come to India to do business with vested interest.  There are many Indians who helped the Europeans to do business, among them one of the important people was Ananda Rangam. He was an interpreter who lived in Pondicherry helped the French  to do business with Indians, the diaries of him reveals  all day to day business activities for a period between 1736 and 1760. His diary was the only written evidence of history for that particular period that is available today.
 
Due to the revolution and advancement  in the printing technologies, lots of books were printed and issued in various languages, people started to learn many things in various fields like art, literature, history, science and technology. 
 
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Ananda Rangam
Archives: The place where all ancient documents are safeguarded.
The National Archives of India (NAI) is one of the biggest Asian Archives of governmental records situated in New Delhi. It keeps communications of past governmental machineries of various departments, which can be used as a Guide. 
 
Tamil Nadu Archives: - One of the largest and oldest archives of South India is Tamil Nadu Archives located in Chennai. Almost all records are present in English, but also it has few records written in other languages as well such as Dutch, Danish, Persian and Marathi, Portuguese, Tamil and Urdu. Some examples from Tamil Nadu archives are as given below:
  • Dutch records (164 Volumes): 1657 to 1845 related to Cochin and Coromandel Coast.
  • Records of Danish from 1777 to 1845.
  • Henry Dodwell was an acting Vice Principal from Teachers College, Saidapet was appointed as a Curator, Madras Record Office. He was assigned to prepare the Calendars of the old records by the British government. He completed it with great effort and published it in 1917. He is considered as the Guardian of the Records.
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Tamil Nadu Archives
Material Sources
Details of famous historical persons and national leaders who belong to modern Indian history can be perceived from paintings and sculptures. Historical buildings like St. Francis Church at Cochin, St. Louis Fort at Pondicherry, St. George Fort in Madras, and St. David fort in Cuddalore, India Gate, Parliament House, and President House in New Delhi, etc portray the different forms and techniques of Indian architecture.
 
The antiquities that are collected and safeguarded in museums help us to nurture our cultural inheritance. Among various articles “Coins” are the important evidence which provides information on important events such Wars and Victories, achievements and functioning of government. As far as the Indian modern coinage is concerned it starts from 1862. There are coins issued by Queen Victoria and Edward VII and many others, those coins bore the faces of them. The Reserve Bank of India was set up in 1935, it is the only authorized government establishment which prints and issues the Coins and Currencies for the Government of India. In January 1938, it printed and circulated the first paper currency “5 rupee note” that bore King George VI.
Reference:
https://www.rarebooksocietyofindia.org/photo_archive/196174216674_453563846674
https://th.thgim.com/migration_catalog/article10412378.ece/ALTERNATES/FREE_660/18MP_TAMIL_NADU_ARCHIVES