Robert W. Wood | |
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 Wood c. 1910 | |
| Born | Robert Williams Wood May 2, 1868 Concord, Massachusetts, U.S. |
| Died | August 11, 1955(1955-08-11) (aged 87) Amityville, New York, U.S. |
| Education | Roxbury Latin School |
| Alma mater | |
| Known for | |
| Awards |
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| Scientific career | |
| Fields | Physics |
Robert Williams Wood (May 2, 1868 – August 11, 1955) was an American physicist and inventor who made pivotal contributions to the field ofoptics. He pioneeredinfrared andultraviolet photography. Wood's patents and theoretical work inform modern understanding of the physics ofultraviolet light, and made possible myriad uses of UV fluorescence which became popular afterWorld War I.[1][2][3][4] He published many articles onspectroscopy,phosphorescence,diffraction, andultraviolet light.
Robert W. Wood was born inConcord, Massachusetts to Robert Williams Wood, Senior. His father had been born in Massachusetts in 1803 and worked as a physician in Maine until 1838, then as a physician and pioneer in the sugar industry on theHawaiian Islands until 1866. He was also active in the American Statistical Association.[5]: 327 Wood junior attendedThe Roxbury Latin School initially intending to become a priest. However, he decided to study optics instead when he witnessed a rare glowingaurora one night and believed the effect to be caused by "invisible rays". In his pursuit to find these "invisible rays", Wood studied and earned several degrees in physics fromHarvard University and theMassachusetts Institute of Technology.[citation needed]
As a student at Harvard he swallowed marijuana as part of a self experiment, recorded the hallucinations he experienced in a report for a course of psychology. A New York newspaper published the report.[5]: 335 After he had received a bachelor’s degree in chemistry there, he continued at Johns Hopkins University[5]: 327 and in 1892 he changed to theUniversity of Chicago. In 1894 he went to theBerlin University to continue chemistry, and underHeinrich Rubens’s influence changed permanently to a career in physics. In 1896, he returned to the US, first the Massachusetts Institute of Technology andin 1897 as an instructor at theUniversity of Wisconsin.[5]: 328
After 4 years at theUniversity of Wisconsin and afterHenry Augustus Rowland's death, he was only 33 years old and yet appointed as his successor atJohns Hopkins University and full-time professor of "optical physics" at Johns Hopkins University from 1901 until his death. He worked closely withAlfred Lee Loomis atTuxedo Park, New York.[6][7]
In early 1900 he visited the United Kingdom giving a lecture at the Society of Arts in London on the diffraction process of photography in colours.[8]
Early in 1902, Wood found that the reflection spectra of subwavelength metallic grating had dark areas.[9] This unusual phenomenon was named Wood's anomaly and led to the discovery of thesurface plasmon polariton (SPP), a particular electromagnetic wave excited at metal surfaces.
In 1903 he developed afilter,Wood's glass, that was opaque to visible light but transparent to both ultraviolet andinfrared, and is used in modern-dayblack lights.[10] He used it for ultraviolet photography but also suggested its use for secret communication.[10] He was also the first person to photograph ultravioletfluorescence.[10][11] He also developed an ultraviolet lamp, which is widely known as theWood's lamp in medicine. The slightlysurreal glowing appearance of foliage in infrared photographs is called the Wood effect.[12]
In 1904, Wood disproved the existence of so-calledN-rays. The French physicistProsper-René Blondlot claimed to have discovered a new form of radiation similar toX-rays, which he named N-rays. Some physicists reported having successfully reproduced his experiments; others reported that they had failed to observe the phenomenon. Visiting Blondlot's laboratory at the behest of the journalNature, Wood surreptitiously removed an essentialprism from Blondlot's apparatus during a demonstration. The alleged effect was still reported, showing that N-rays had been self-deception on Blondlot's part.[13]
Wood identified an area of very low ultravioletalbedo (an area where most of the ultraviolet was absorbed) in theAristarchus plateau region of theMoon, which he suggested was due to highsulfur content.[14] The area continues to be called Wood's Spot.[15]
In 1909, Wood constructed the first practicalliquid mirror astronomical telescope, by spinningmercury to form aparaboloidal shape, and investigated its benefits and limitations.[16] Wood has been described as the "father of both infrared and ultraviolet photography".[10] Though the discovery ofelectromagnetic radiation beyond thevisible spectrum and the development ofphotographic emulsions capable of recording them predate Wood, he was the first to intentionally produce photographs with bothinfrared andultraviolet radiation.[11] In 1938, he officially retired and was then appointed Research Professor, a position he kept until his death.
Both before and after his retirement Wood took part in several police investigations, including theWall Street bombing.[11] His investigations into the "Candy-Box Murder", a 1930 bombing that killed 18-year Naomi Hall Brady and two of her siblings at her home inSeat Pleasant, Maryland, helped convict her brother-in-law Leroy of manslaughter.[11][17] The bizarre death of 51-year-old socialite Katherine Briscoe at herBaltimore home in 1934 from a carelessly discardedblasting cap and his experiments derived therefrom would lead to the first scientific publication onexplosively formed penetrators in theProceedings of the Royal Society in 1936.[11][18][19]
Wood also authored nontechnical works. In 1915, Wood co-wrote a science fiction novel,The Man Who Rocked the Earth, along withArthur Train.[20] Its sequel,The Moon Maker, was published the next year.[21] Wood also wrote and illustrated two books of children's verse,How to Tell the Birds from the Flowers (1907), andAnimal Analogues (1908).
In 1892, Wood married Gertrude Hooper Ames in San Francisco. She was the daughter of Pelham Warren and Augusta Hooper (Wood) Ames, and the granddaughter ofWilliam Northey Hooper and theMassachusetts Supreme Court justice Seth Ames.[22] She was his "constant companion for more than 60 years, although she herself had no interest in scientific things" , in Baltimore, at their summer place near Easthampton on Long Island, and during their travels abroad. They had a very wide circle of friends. His wife provided "stability without which a man of Wood’s temperament might have found life occasionally very difficult". They had three children.[5]: 338
Wood had a heart attack a few years before[5]: 337 he died during his sleep without any severe illness[5]: 327 inAmityville, New York.[22]
Although physical optics and spectroscopy were Wood's main areas of study, he made substantial contributions to the field ofultrasound as well. His main contributions were photographing sound waves and investigating high-power ultrasonics.
His first contribution to the field of ultrasonics was the photography of sound waves. Wood's primary research area was physical optics, but he found himself confronted with the problem of demonstrating to his students the wave nature of light without resorting to mathematical abstractions which they found confusing. He therefore resolved to photograph the sound waves given off by an electric spark as an analogy to light waves.[23] An electric spark was used because it produces not a wave train, but asingle wavefront, making it much more intuitive to study and visualize. Although this method was first discovered byAugust Toepler, Wood did more-detailed studies of the shock waves and their reflections.[24]
After these early contributions Wood returned to physical optics, setting aside his interest in "supersonics" for quite some time. With the entry of the United States intoWorld War I, Wood was asked to help with the war effort. He decided to work withPaul Langevin, who was investigatingultrasound as a method for detectingsubmarines. While in Langevin's lab, he observed that high-poweredultrasonic waves can cause theformation of air bubbles in water, and that fish would be killed or an experimenter's hand would suffer searing pain if placed in the path of an intense sound beam. All of these observations piqued his interest in high-powered ultrasound.
In 1926, Wood recounted Langevin's experiments toAlfred Lee Loomis, and the two of them collaborated on high intensity ultrasound experiments; this turned out to be Wood's primary contribution to the field of ultrasonics.
The experimental setup was driven by a twokWoscillator that had been designed for a furnace, allowing for the generation of very high output power. The frequencies they used ran from 100 to 700 kHz.[25] When thequartz platetransducer was suspended in oil, it would raise a mound of oil up to 7 centimetres (3 in) higher than the rest of the surface of the oil. At lower powers, the mound was low and lumpy; at high powers, it would rise up to the full 7 cm, "its summit erupting oil drops like a miniature volcano".[25] The airborne oil drops could reach heights of 30–40 centimetres (12–16 in). Similarly, when an 8-centimetre (3 in) diameter glass plate was placed on the surface of the oil, up to 150 grams (5 oz) of external weight could be placed on top of the glass plate, supported by the strength of the ultrasound waves alone. This was achieved by the waves reflecting and re-reflecting between the transducer and the glass plate, allowing each generated wave to impart its force to the glass plate multiple times.
When attempting to take the temperature of the mound of erupting oil with a glass thermometer, Wood and Loomis accidentally discovered another set of effects. They noted that although the mercury in the thermometer only indicated 25 °C (77 °F), the glass felt so hot that it was painful to touch, and they noticed that the pain became unbearable if they tried to squeeze the thermometer tightly. Even if very fine thread of glass only 0.2 millimetres (0.01 in) in diameter and 1 metre (3 ft 3 in) long was put in the oil at one end, holding a bulge in the glass at the other end still resulted in a groove being left in the skin and the skin being seared, with painful and bloody blisters forming that lasted several weeks, showing that the transmitted ultrasound vibrations generated were quite powerful.[25] When a vibrating glass rod was placed lightly in contact with driedwoodchips, the rod would burn the wood and cause it to smoke; when pressed against a woodchip it would quickly burn through the chip, leaving behind a charred hole. All the while the glass rod remained cool, with the heating confined to the tip. When a glass rod was pressed lightly against a glass plate it etched the surface, while if pressed harder it bored right through the plate. Microscopic examinations showed that the debris given off included finely powdered glass and globules of molten glass.[25]
Wood and Loomis also investigated heating liquids and solids internally using high intensity ultrasound. While the heating of liquids was relatively straightforward, they were also able to heat anice cube such that the center melted before the outside. The ability to heat or damage objects internally is now the basis of moderntherapeutic ultrasound. Turning their attention to the effects of high-intensity ultrasound on living matter, Wood and Loomis observed ultrasound tearing fragile bodies to pieces. Cells were generally torn apart at sufficiently high exposure, although very small ones like bacteria managed to avoid destruction. Frogs, mice, or small fish were killed after one to two minutes of exposure, replicating Langevin's earlier observation.[25]
Wood and Loomis also investigated the formation ofemulsions andfogs,crystallization andnucleation,chemical reactions,interference patterns, andstanding waves in solids and liquids under high-intensity ultrasound. After completing this broad array of experiments,[when?] Wood returned to optics and did not return to ultrasonic work. Loomis would go on to advance the science further with other collaborators.[26]
