Thursday, October 6, 2011

Stunning! Aurora Borealis in the Finnish Lapland [Video]

The term aurora borealis means "dawn of the north." Aurora australis means "dawn of the south." These fantastic light displays are produced by collisions between electrically charged particles from the sun as they enter Earth's atmosphere near the magnetic poles, where Earth's protective magnetic field is weakest. In most instances, northern and southern auroras are mirror images of each other that occur at the same time.

This film was shot in Finnish Lapland in 2011.  (H/t: Flatlight Films; Geeks are Sexy; Northern Lights Centre)

Monday, March 28, 2011

The Crookes Railway Tube

PV Scientific's founder and master instrument maker, Jim Hardesty, in his laboratory 
with a beautiful old Crookes railway tube, also known as a paddlewheel tube.
Photo credit: Bryan T. Root, Motherlode Pictures.

During the 1870s, the British physicist, Sir William Crookes, performed a number of experiments in which cathode rays seemed to cause the movement of objects suspended in evacuated tubes. In the late 1870s, he developed a tube that provided the most spectacular demonstration of this effect: the railway tube, also known as the paddlewheel tube. This tube contains two concave or focused cathodes, one on either end, so that the polarity of the electricity flowing through the tube can be changed back and forth, and the cathode rays can be aimed at the vanes (or paddles) of mica in a paddlewheel positioned on two glass "rails" within the tube. When the cathode beam strikes the mica vanes, the paddlewheel rolls down the track. When the polarity of the electrical energy being fed into the tube is reversed, the paddlewheel rolls in the opposite direction.

A still photo of the railway tube in operation. The cathode is seen as a purple glow at 
the left. The green rectangles in the center are the glowing vanes, or paddles, spinning as the paddlewheel rolls along the glass "track" of the tube. Photo credit: Bryan T. Root, Motherlode Pictures.

Crookes was certain that the spinning effect of the wheel in the tube was caused by transfer of momentum from the impact of the corpuscles (particles) of the cathode rays, and the railway tube demonstration provided very firm support for the corpuscular theory of cathode rays. However, in 1903, some six years after J. J. Thompson discovered the electron, he wrote about the working of the Crookes railway tube in his famous book, The Discharge of Electricity through Gasses, claiming that the push of electrons alone could not explain the speed of the spinning wheel in the tube, and Thompson offered the idea that the heat generated by the electrons striking the mica paddles expanded the atmosphere on the side of the paddles being struck, thus pushing the paddles forward. Thompson's explanation is also used to describe the action of another invention of Sir William Crookes, the radiometer.

Wednesday, March 9, 2011

Musschenbroek and the First Electrical Capacitor

Pieter van Musschenbroek, 1692-1761
"I wish to inform you of a new, but terrible experiment, which I advise you on no account personally to attempt." 
   ~Pieter van Musschenbroek

March 14th, 2011, marks the 319th anniversary of the birth of Pieter van Musschenbroek, the fellow usually credited with the discovery and initial investigation of the world's first electrical capacitor.

Called the Leyden jar after Holland's University of Leyden where Musschenbroek taught, this instrument was independently discovered at about the same time by Ewald Jurgen von Kleist, a Pomeranian cleric.

Musschenbroek, the son of a scientific instrument maker, was a medical doctor, mathematician, and natural philosopher who spoke at least seven languages and had attended lectures by Isaac Newton and Newton's experimental assistant, John Theophilus Desaguliers, himself famous for his discoveries regarding the properties of electricity.

Before the discovery of the Leyden jar, electrical experimenters were able to generate electricity using early static generating machines, but they were limited in their experimentation because they had no way to store the electricity thus generated. In 1746, Musschenbroek, working with collaborators, was attempting to electrify water when he got the shock of his life, quite literally:

Musschenbroek attempting to electrify water 

Musschenbroek described his experience in a 1746 letter:
"I wish to inform you of a new, but terrible experiment, which I advise you on no account personally to attempt. I am engaged in a research to determine the strength of electricity. With this object I had suspended by two blue silk threads, a gun barrel, which received electricity by communication from a glass globe which was turned rapidly on its axis by one operator, while another pressed his hands against it. From the opposite end of the gun barrel hung a brass wire, the end of which entered a glass jar, which was partly full of water. This jar I held in my right hand, while with my left I attempted to draw sparks from the gun barrel. Suddenly I received in my right hand a shock of such violence that my whole body was shaken as by a lightning stroke. The vessel, although of glass, was not broken, nor was the hand displaced by commotion: but the arm and body were affected in a manner more terrible than I can express. In a word, I believed that I was done for."
What had happened?

Metal and water conduct electricity, but glass does not. When Musschenbroek's assistant rubbed the rotating glass sphere, a positive static charge was generated. As this positive charge traveled up the chain, across the gun barrel, and down the brass wire into the water, it didn't electrify the water quite as Musschenbroek had hoped. Instead, the static charge continued to travel through the water and built up on the inside surface of the glass jar. 

Simultaneously, a negative static charge was being induced on the outside surface of the glass jar in Musschenbroek's right hand, with his body providing a path to ground. 

These opposite static charges were held in equilibrium on opposite sides of the non-conducting glass until, Zap!, Musschenbroek completed the circuit with his own body by touching with his left hand the inside of the glass jar held in his right hand. The result was violent discharge of stored static electricity, much like a lightning bolt.

Soon after, a London experimenter named Dr. John Bevis replaced the two conductors on either side of the glass (the water inside the jar and Musschenbroek's right hand resting on the outside of the jar) with metal sheets wrapped inside and outside of the jar. A cap was added to the jar to secure a metal rod and chain suspended in the jar. In this configuration, the opposite charges on the inside and outside of the glass jar hold each other in equilibrium until a path is provided for their discharge.

The Leyden jar made it possible for early experimenters to conduct a wide range of electrical experiments.

One experimenter who made excellent use of the Leyden jar was Benjamin Franklin, who was the first to understand and explain how the Leyden jar functions. Franklin based his understanding one of his most important scientific observations—that electrical energy has both positive and negative charges.
Series Pair of Leyden Jars with a total capacity of 450 picofarads at 350 kilovolts

Here at PV Scientific Instruments, we offer a wide range of classic Leyden jar capacitors, from static-electrical experimentation types to spark-oscillation transformer types for radio work. 

Wednesday, March 2, 2011

Lightning Flashing on Saturn

This image from NASA's Cassini spacecraft -- the first of its kind -- shows lightning on Saturn's night side flashing in a cloud that is illuminated by light from Saturn's rings.

The cloud, whose longest dimension is about 3,000 kilometers (1,900 miles), does not change perceptibly over the 16 minutes of observations covered by the 10-second movie. The lightning flashes are the bright spots within the cloud, and are about 300 kilometers in diameter. The lightning strikes last for short periods of time (less than one second before the time line of the movie was compressed).

The energy output of the visible light from the lightning is comparable to the brightest lightning flashes on Earth.

At Saturn, there are three types of clouds that might produce lightning. The top layer is made of ammonia ice; the middle layer is made of a compound of hydrogen sulfide and ammonia; the bottom layer is water. The light has to diffuse up through this cloud system, which is over 100 kilometers (60 miles) thick. The width of the lightning spot at the top of the cloud is proportional to the depth where the flash originated. The observed widths indicate that the lightning is originating either in the hydrogen-sulfide-ammonia cloud or in the water ice cloud. The lightning does not appear to originate at the deepest levels of the cloud system, where water is liquid.

Interested in how early researchers came to understand lightning? PV Scientific offers reprints of classic texts on the subject of atmospheric electricity on our Classic Reprint Page.

Wednesday, February 23, 2011

Women in Radio: Mary Texanna Loomis

Mary Texanna Loomis with wireless equipment she built

Sitting on my desk these days is a well-worn burgundy-red copy of an unusual book: a wireless textbook written by a woman: Radio Theory and Operating for the Radio Student and Practical Operator, by Mary Texanna Loomis.
My copy, the fifth (1930) edition, is also unusual in that it once was the property of a female amateur radio operator, Lena E. Kay (Mrs. Arthur Kay), whose call sign was W5HLI, which indicated that Lena got her amateur radio license in U.S. District 5, that is, in Arkansas, Louisiana, Mississippi, New Mexico, Oklahoma, or Texas. If you’d like to track down a radio call sign, the information at this link will help.

Reading Mary Texanna Loomis's 1,000-page book was no lightweight adventure--in more ways than one. Radio Broadcast magazine considered it “one of the most comprehensive volumes in its field” because it covered not only the radio theory and circuits of interest to amateur radio enthusiasts like Lena Kay, but because it also served as an electrical engineering textbook for future operators of radio telegraphs and radio telephone transmitters and receivers.

Mary Texanna Loomis was well prepared to write her textbook: she had founded Loomis Radio College in Washington, D.C., where she spent 12 to 15 hours a day studying, teaching, and writing about radios. The Loomis Radio College offered a six-month course leading to a first class commercial radio license and eventually a four-year course leading to a degree in Radio Engineering. From Wiccanpiper at everything2:
Miss Loomis also intended that her students understand more than just the inner and outer workings of radio. In addition to a radio laboratory (with equipment constructed almost entirely by Miss Loomis herself), the school maintained a complete shop capable of teaching carpentry, drafting, and basic electricity. She reasoned that many of her graduates might find themselves at sea, or in other challenging situations, and she wanted them adequately prepared. "No man", Miss Loomis said at the time, "can graduate from my school until he learns how to make any part of the apparatus. I give him a blueprint of what I want him to do and tell him to go into the shop and keep hammering away until the job is completed."
Mary Texanna Loomis teaching at the Loomis Radio College, circa 1920

With that kind of experience and attitude, it is no wonder that Radio Theory and Operating was, above all, an excellent reference for wireless telegraph operators. From the May 1928 issue of Radio Broadcast:
Miss Loomis’s book is to be recommended particularly to commercial wireless telegraph operators. The chapters dealing with the care of storage batteries, the functioning and care of motor generators and power equipment, and the regulations applying to commercial practice are thorough and complete. An extensive series of questions at the back of the book are helpful in preparing for Government examinations. Standard ship and commercial installations are quite thoroughly dealth with.
Mary Texanna was delighted to discover that she was related to Dr. Mahlon Loomis, the American electrical experimenter who was the first to send and receive wireless signals in about 1865, who was the first to use vertical antennas, and who received a letters patent for his system of "aerial telegraphy" in 1872.

This wireless-education pioneer was born on August 18, 1880 on a homestead near Goliad Texas. When she was three, her parents, Alvin Isaac and Caroline, returned to Rochester, NY and then moved to Buffalo, where her father became president of a large delivery and storage company. She later lived in Virginia. Mary Texanna was well educated and spoke French, German, and Italian as well as English. During WWI she became interested in the new field of wireless and in 1920, at the age of 40, established her school at 401 Ninth St., NW in Washington. (The school had it's own experimental license, 3YA.)

In 1938, she retired to San Francisco, where she established herself at the historic "Grand Dame" of Union Square, the St. Francis Hotel, and listed her occupation as stenographer. Mary Texanna Loomis died in 1960 at the age of 80.