Archive for the ‘Science & Technology’ Category

Semaphore Towers ~ A Pre – Telegram Communication System

July 17, 2013 46 comments

Semaphore Towers

A Pre – Telegram Communication System

Its a typical rural Bengal landscape, a villager makes is way through agricultural fields, but the chimney like structure is definitely unique. Its not a chimney of the brick kilns that dot the Bengal rural landscape nor is it a wtach tower used to keep eye on invading Bargi (Maratha).

Semaphore Tower, Parbatichak, Arambagh, Hooghly, West Bengal
Semaphore Tower, Parbatichak, Arambagh, Hooghly, West Bengal

Its a semaphore tower, quiet a few of which still dot the rural as well as urban landscapes of West Bengal, Bihar and Jharkhand.

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Transition of Venus and the Birth of Cinema

July 4, 2012 4 comments

6 June 2012 5:00 am Kolkata. I was up in my Saltlake terrace to witness the sunrise, yes sunrise. But it was no ordinary sunrise it was something special, very special, something that wont be witnessed in the next 117 years!!!!!

Transit of Venus (The tiny black spot on the 9 'O clock position of the solar disc is Venus). Shot just after sunrise from Calcutta

Transit of Venus (The tiny black spot on the 9 ‘O clock position of the solar disc is Venus). Shot just after sunrise from Calcutta

Yes you have probably got it by know I was about to witness a rarest of rare celestial event, the transition of Venus. It was well past the schedule sun – rise time but the sun was yet to be seen in the heavily polluted sky above the concrete jungle of Saltlake.

Pierre Jules Cesar Janssen (Sketch Courtsy: Biamn B Nath)

Pierre Jules Cesar Janssen (Sketch Courtsy: Biman B Nath)

It was almost 5:30 am more than a half an hour after schedule sunrise time I got the first glimpses of the sun. It was partially covered by clouds but soon the whole disc of the rising sun emerged out of the clouds. I pointed my Nikkon D60 DSLR fitted with the Sigma 70 – 300 mm (no filter was required) lens and zoomed in at the maximum level and clearly a dot was visible at the 9 O clock position. Yes it was Venus, walking along the disc of the sun.

As I photo documented the rare celestial event, using a x – ray plate as makeshift filter, I was transported back in time and back in 1874 when French scientist Pierre Jules Cesar Janssen also photographed the transition of Venus using a new photographic technique.

The root of the story goes back to early 18th century when Edmund Halley, of Halley’s comet fame, came up with the theory of measuring the distance between the Sun and Earth (Astronomical Unit) by taking advantage of the transition of Venus.

But transition of Venus was not a regular event and Halley left for the heavens in in 1742, 19 years before the next transition of Venus was to take place. Halley used the concept of parallax during the transition of Venus to accurately measure the astronomical unit (AU). Halley wanted to place two observer in the same longitude maintaining a maximum North – South distance, thus taking maximum advantage of the parallax error.

During the next transition of Venus in 1761 voyages were sent all over the world carry out Halley’s experiment. But the scientist came across a strange problem!!!!. It is understood that a exact time of the Venus entering the Sun’s disk is to be noted. But the scientist observed that the circular dot of Venus turned into a water drop shape the moment it entered the solar disc. The phenomena was not only unexplained but also unexpected but it prevented the accurate time keeping and in the proses failed to fined the accurate value of AU.

The phenomena came to be known as “Black Drop Effect” and the scientist were unable to come up with any solution for the next transition in 1769.

Janssen's 48 frames (Each teeth like structure represents the portion of the solar disc with Venus as a dot) (Image Courtsey: Desh)

Janssen’s 48 frames (Each teeth like structure represents the portion of the solar disc with Venus as a dot) (Image Courtesy: Desh)

For the transition of Venus in 1874 the scientist were more prepared not only they had more advance telescope but they had a new weapon in their armory – PHOTOGRAPHY!!!! Photography was the the most powerful tool of measuring and recording the exact moment of the transition. But shooting multiple frames in a short span of time was something unknown at that time.

Enter Pierre Jules Cesar Janssen, the French scientist who inspired by Samuel Colt’s revolver design, developed the PHOTOGRAPHIC REVOLVER which shot 48 frames in 72 second. Janssen discover not only solve the problem of “black drop” but helped to measure the value of AU with great accuracy. But the story continued and two decades later the Lumiere brothers, used Janseen idea to create the first movie camera leading to the invention of cinema.

“Necessity is the mother of invention” goes an old saying and it is hard to believe that a scientific need of observing a rare celestial event can lead to the discovery of the most popular source of entertainment in the modern world.

As I stood on my Saltlake terrace wondering about the strange coincidence Venus was well into her walk along the solar disc. It was time for another black drop and time for Venus to bid good bye to the Sun only to return after 117 years!!!!!


Special Thanks:

  • Prof Biman B Nath: Baman B Nath is a professor of astrophysics at the Raman Research Institute, Bangalore. A talented artist Baman (da) has provided me not only with the sketch of Pierre Jules Cesar Janssen but also provide valuable inputs regarding the transition of Venus.
  • Prabir Biswas: Fellow photographer and armature sky watcher, Prabir (da) has provided me valuable tips for photographing the transition of Venus.

Potter’s Wheel ~ A brief history

April 18, 2012 3 comments

Pottery, the art of making pots out of burnt clay, is an ancient art. Pieces of pottery are inevitable parts of an archeological digs all over the world. The oldest evidence of pottery dates back to 10,000 BC in Japan. The concept of clay made vessels sprung up when the society shifted from nomadic to agrarian. The society was in need for stable but heavier containers, leading to the art of pottery.


Spinning the potter's wheel with a stick

Spinning the potter’s wheel with a stick

Before the invention of the wheel, pots were shaped by coiling clay and then turning it repeatedly by hand. The disadvantage of this method is that a single vessel could take quite awhile to create. As society grew and trade and commerce flourished the demand of clay made vessel grew. The old method for making pots gradually became insufficient for keeping up with the demand.

As the demand for pots increased, number of methods were developed to increase the coiling process. Some potters used a platter (slow wheel) that could be easily turned as a surface for coiling pots. This prevented the potter from moving round the pot, thus saving time to some extent.

The wheel was invented in ancient Mesopotamia (present-day Iraq) around 3,000 B.C. Within a short time, the Sumerians adapted the wheel concept to a faster method of turning and shaping pottery. These first turntables were slow, but they were a vast improvement over the previous methods of shaping pots.

With the mass scale production of pots the pot making soon turned into an industry. An ancient Egyptian Hieroglyphics on a tomb wall records the mass scale production by use of potter’s wheel.

Soon techniques were adopted to make the wheel faster and smoother, thus increasing the potter’s ability to make finer clay vessels with sterns, smooth spirals and true circles.

A typical potter's workshop

A typical potter’s workshop

In the 19th century the concept of throwing pottery, as we know it today, flourished due to potter’s wheel that could achieve higher spinning speed. This is partially due to the French development of momentum wheel . a wheel that took advantage of low friction and high weight to achieve speed.

Today the potter’s wheel have been fitted with ball bearing and is run by electricity but the basic principle remains the same.

The following photos were shot in the People Institute of Development and Training (PIDT) workshop in Madhupur, Jharkhand. I was invited in this worshop to deliver a presentation on the terracotta temples.


Special Thanks:

  • Ms Indira Dasgupta and all the master craftsmen, staff and members of PIDT.