Henry's Accomplishments

The turning point in Henry’s career came in 1904, when as co-president, he was expected to deliver an address to the Australasian Association for the Advancement of Science. He needed to decide which topic he would speak on, and hearing of the recent breakthroughs in radioactivity by Antoine-Henri Becquerel and Marie and Pierre Curie, he felt this would make a suitable discussion. This prompted Henry to study more deeply into the subject himself, and was the defining moment in his becoming the renowned physicist he is remembered as today. Henry’s first area of research was the penetration of alpha and beta particles into gaseous media. He observed that alpha particles, unlike beta and gamma particles, would move undeviated through a gas until

In this he showed also that this definite range, or “stopping power”, of a substance is proportional to the square root of its atomic number, and was the first to distinguish between four groups of alpha particles—those emitted by radium, radon, RaA, and RaC. Henry’s work continued with the study of the ionization of gases by alpha particles, and earned him a fellowship of the Royal Society of London. It should be noted that all of Henry’s initial work however was not all glory, as he became a center of controversy for several years concluding that X-rays and gamma rays were not electromagnetic waves, but rather streams of neutral particles. As experimental evidence arose which was in clear opposition, however, he of course adopted the new understandings. Nonetheless, Henry’s contributions had already earned him respect in the worldwide science community. In 1909, Bragg left his position at Adelaide to become the Cavendish Chair of Physics at the University of

Henry had married Todd’s daughter, a skilled water-colorist, with whom he fathered a daughter and two sons—one being Lawrence, and the other later killed at Gallipoli, a World War I conflict. Not surprisingly, Lawrence followed directly in his father’s footsteps; he was recognized as a child prodigy, and proceeded to enroll in the University of Adelaide at the age of just fifteen. Here, he too earned a degree in mathematics with first-class honors in 1908. During this time, Lawrence had done a great amount of observing and assisting in his father’s research (broken bones were no longer a prerequisite), and having gained much experience, left Adelaide upon graduation to pursue his graduate studies in physics at Trinity College, Cambridge. It seems to be no coincidence that it is at this time also that Henry left Adelaide to become a professor at an English university. Lawrence earned first-class honors in the Natural Science Tripos, similar to his father, and by 1912 had published his first and very own paper in the journal Proceedings of the Cambridge Philosophical Society. The topic of the paper was the examination of the recent von Laue phenomenon—the appearance of a diffraction pattern of X-rays through a sodium sulfate crystal. At the time, nearly two decades after Rontgen’s discovery of X-rays, the nature of the radiation remained undetermined. Many physicist’s suspected them to be electromagnetic waves and