Bonn—the leading spectroscopist in Germany—and Otto
Lummer, a famous physicist from Breslau University.
Upon his return to Hopkins, Wood moved his spectroscopic apparatus to a room in the astronomy tower that contained
the Johns Hopkins astronomical telescope. Lacking sufficient
intensity in his electric arc light source, Wood thought he
would try sunlight. The sun has been used as a source in many
developments in physics and medicine: Newton spectrally dispersed sunlight with a prism; Raman discovered his effect with
a heliostat; and the German ophthalmologist Gerhard Meyer-Schwickerath used the sun as the light source when developing
the first retinal photocoagulators.
In his new laboratory venue, Wood designed and constructed a spectrograph; it had three large prisms of flint glass
and large achromatic lenses. He mounted a heliostat on the
window sill and focused the sunlight on the entrance slit of a
monochromator. The emerging light from the exit slit was then
focused on the sodium vapor in the quartz tube, and the fluorescence from the sodium vapor was directed onto the entrance
slit of his newly constructed monochromator with a mirror and
condensing lens.
Wood could then alter the excitation light by turning the
prisms in the excitation monochromator. He could either visually observe the spectrum of the sodium vapor or capture it on
a photographic plate attached to the spectrograph. With this
apparatus, he would make a major discovery: He could detect
and measure various groups of widely separated lines in a complex spectra that consisted of thousands of closely spaced lines.
René Blondlot and N-rays
Wood gained a reputation as a skeptic and debunker of theories that did not hold up to close scientific scrutiny. Perhaps
the best example is his work to disprove Blondlot’s theory of
so-called N-ray radiation. That story began in 1903, when
the French physicist René Blondlot was investigating whether
X-rays were particles or electromagnetic waves. Blondlot was
the chair of the department of physics at the University of
Nancy, a noted expert on electromagnetic radiation, and a
member of the French Academy.
Blondlot knew that electromagnetic waves could be polarized, and he planned to use this characteristic to determine the
nature of X-rays. He used a spark between two parallel wires
as the detector; at the proper orientation of the detector, the
polarized electromagnetic waves should increase the intensity
of the sparks. Blondlot observed that a quartz prism could bend
(refract) the electromagnetic waves that interacted with the spark
detector. From the observed properties of the radiation, which
differed from those of X-rays, Blondlot reasoned that, if the
rays were not X-rays, they must constitute a new type of ray.
He named them N-rays after the University of Nancy.
Blondlot described his experiments in a series of papers
published in the French Academy’s Comptes rendus. He alleged
that many metals spontaneously emit N-rays and that they
could be detected with a very weakly illuminated piece of
AIP Emilio Segré Visual Archives
Wood viewing his
rotating mercury
mirror in rotation.
The distortion is
astigmatism due
to the oblique
incidence.
paper. N-rays could supposedly be transmitted through metal, wood and paper, but not water. They were readily transmitted through materials that are opaque to visible light; however,
water and rock salt were opaque to them. Blondlot claimed
that there were many sources of these N-rays: the Nernst glower (used in home lighting at that time), heated pieces of silver
and sheet iron. The Bunsen burner did not produce N-rays.
Blondlot claimed that the sun was a source of N-rays as well.
Subsequently, many Frenchmen claimed priority in the discovery of N-rays. But Blondlot prevailed, in spite of skepticism
from many of the world’s scientists due to their inability to
reproduce the reports. In 1904, the French Academy awarded
Blondlot the Prix Leconte; it was given to him for his entire
corpus of research; the discovery of N-rays was only mentioned
at the end of the list of his achievements.
Within a year of the purported discovery, 12 N-ray papers
appeared in Comptes rendus. Shortly afterwards, Blondlot
reported that he had constructed a spectrometer with aluminum lenses and an aluminum prism. He said that N-rays
showed dispersion (they are composed of various wavelengths)
and that he had measured their wavelengths.
Jean Becqueral, the son of Henri, asserted the N-rays could
be transmitted over wires. Soon many biologists, psychologists
and others made exciting claims: nerves in the spinal cord
emitted N-rays that could be used to detect disease. A fellow
faculty member, Augustin Charpentier, stated that N-rays were
emitted in human nerves and muscles and even in the human
body after death. He reported an increase in N-ray intensity
with motor activity and proposed a new approach for cardiac
imaging. Others detected N-rays in plants. In the first six
months of 1904, Comptes rendus published more than 100
papers on the new rays. Twenty French scientists claimed that
they had confirmed their existence.
Meanwhile, others scientists, including Wood, could not
detect the new form of radiation. Wood, who was a foreign
member of the Royal Society of London, traveled to Nancy with
the purpose of validating Blondlot’s claims. Wood was shown
a series of experiments intended to convince him of the reality
of N-rays. First, Blondlot shared with him photographs that
purported to demonstrate their existence. He observed that
