Today, Austrian physicist Victor Hess is largely credited with the discovery of cosmic rays. In the early part of the 20th century, the large amount of ionising radiation in the Earth's atmosphere caused a great deal of head-scratching. 

Domenico Pacini at the Italian Agency of Meteorology and Geodynamics made the same discovery at the same time with a slightly different method. Both men were aware of each other's work but that their scientific legacies are very different. "While Hess is remembered as the discoverer of cosmic rays, the simultaneous discovery by Pacini is forgotten by most," 
 
Why ??? . Pacini died in 1934. Two years later, the Nobel Prize for Physics (which cannot be awarded posthumously) was given to Hess for his work on the discovery of cosmic rays.
 
The Report "Il Nuovo Cimento" is  published by the Italian Physical Society ( Societa Italiana di Fisica ) founded in 1844. http://www.sif.it/SIF/en/portal/journals/ncc#top   The Date of the Critical Report is Unknown. 

Pacini  took the degree in Physics at the University of Rome in 1902. Assistant at the "Regio Ufficio Centrale di Meteorologia e di Geodinamica" (Italian Agency of Meteorology and Geodynamics) from 1905 to 1927. Professor of Geophysics from 1915 to 1925 (University of Rome), then professor of Experimental physics in 1928 at the University of Bari.

It was observed that an electroscope in a vessel at earth potential gradually lost its charge, even if very carefully insulated, due to gaseous ions. Pacini observed simultaneous variations of the rate of ionization on mountains, over a lake, and over the sea. Pacini concluded that a certain part of the ionization must be due to sources other than the radioactivity of the Earth or the air.

Pacini was a Full Professor for ten years before Hess was (1915 - 1925). 

The history of science is littered with injustices and today Alessandro De Angelis at the University of Udine in Italy outlines another associated with the discovery of cosmic rays .

Today, the person largely credited with the discovery of cosmic rays is the Austrian physicist Victor Hess. In the early part of the 20th century, the large amount of ionising radiation in the Earth's atmosphere caused a great deal of head-scratching. 

The world's physicists naturally assumed that the origin of this radiation was the Earth's crust but were puzzled by measurements that seemed to show that radiation levels increased higher up in the atmosphere.

Hess developed a technique for measuring radiation levels with much greater accuracy and then flew himself and his apparatus by balloon to altitudes of over 5 kilometres to take measurements. The data revealed that radiation levels at 5km were about twice as high as at sea level. 

Hess rightly concluded that the Earth could not be the source of this radiation, which was later christened cosmic rays.

But Hess wasn't the only one working on this problem. De Angelis points out that the Italian scientist Domenico Pacini at the Italian Agency of Meteorology and Geodynamics made the same discovery at the same time with a slightly different method. Instead of flying his measuring apparatus at altitude, Pacini placed it in a copper box and submerged it in the salty waters of the Bay of Livorno. 

He found that the intensity of radiation underwater was significantly less than at the surface and concluded, like Hess, that it could not be coming from the Earth. De Angelis has even unearthed the paper in which Pacini published this work and offers the first English translation on the arXiv. 

De Angelis points out that both men were aware of each other's work but that their scientific legacies are very different. "While Hess is remembered as the discoverer of cosmic rays, the simultaneous discovery by Pacini is forgotten by most," he says. 

Google confirms this assertion with blunt ignominy. While typing the phrase "Victor Hess" into the search engine gives you over 900,000 results, doing the same for "Domenico Pacini" gives only 90,000, the first of which is the question "Did you mean: Domenico Pacitti".

It's not hard to understand why. Pacini died in 1934. Two years later, the Nobel Prize for Physics (which cannot be awarded posthumously) was given to Hess for his work on the discovery of cosmic rays.

Ref: arxiv.org/abs/1002.1810: Penetrating Radiation At The Surface Of Water

http://www.technologyreview.com/blog/arxiv/24805/

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