Invisible Light

The Remarkable Story of Radiology

Adrian Thomas

• Publisher: CRC Press
• Year: 2022
• Print ISBN: 9780367344269
• eBook ISBN: 9781000556452
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Medical Theory, Practice & Reference
• Index: Biological Sciences

The book is a developed history of the radiological sciences – covering the back-story to Röntgen's discovery, the discovery itself and immediate reception the early days of radiology leading to classical radiology (the pre-digital world). The 1970s as the 'golden decade' of radiology will be covered in detail, with the development of CT, MRI and modern interventional radiology. It will appeal to interested members of the public, to those working in the field, and to historians of medicine and science.

Key Features:

• Accessible and engaging, even for readers without any formal scientific training or education

• Authored by an authority in the field

• Contains previously unpublished materials from the author's extensive personal library and archive

1 Röntgen’s Discovery and Its Background

DOI: 10.1201/9780429325748-1

Introduction

Röntgen’s discovery was momentous and following it nothing was quite the same again. It is now difficult to put ourselves into the mindset of those whose worldview was formed before the discovery. The reverberations were felt in the scientific, medical, and artistic communities and helped to bring in the modern world. There were two streams necessary for the discovery to take place, and these were the electrical and the photographic, and Röntgen was expert in both. In the medical discipline of radiology, these two streams continued separately for many decades, coming together with the advent of digital imaging.

Röntgen made his discovery whilst passing an electrical current across an evacuated glass bulb, a discharge tube. His discovery was the result of systematic and careful research by Röntgen and those who went before him. The discovery was not an accident in the accepted meaning of the word.

For X-rays to be produced, the first requirement is for an electrical current of sufficiently high energy to overcome the high electrical resistance offered by the vacuum in a glass bulb. To obtain this high-tension current, various transformers were designed. The second requirement is the means of producing a vacuum, and this was extraordinarily difficult. We take the glass bulb enclosing a vacuum, such as in the simple incandescent light bulb, so much for granted that we forget what a major technological achievement it was. It was the development of the mercury pump that made possible the manufacture of the vacuum tube and resulted in the production of X-rays. Finally, it was Professor Herbert Jackson (1863–1936) of King’s College, London, designed the focus vacuum tube, which enabled the cathode rays to be focused onto a metal target, and produced the first real X-ray tube.

Early History

Electrical phenomena are complex and difficult to understand. Early humans would have observed these strange phenomena, such as lightning or the polar lights (the aurora polaris), northern lights (the aurora borealis) (Figure 1.1), or southern lights (the aurora australis) and then speculated as to their origins. The pages of antique history abound with references to the symbolic associations that were established between myth and legend on the one hand and such elementary phenomena on the other. Humanity was ever ready to attribute the mystery of flash and sound to supernatural powers, so the earliest electrical observations were invested with a sacred or religious character. Even an apparently simple question regarding the nature of light was to open fascinating avenues for discovery. In reality, humans do not change, and whilst we may smile at attributing thunder and lightning to the actions of the gods, many contemporary writers, including Fritjof Capra¹ and Rob Bell,² now derive a spirituality from the universe of quantum physics.

FIGURE 1.1 The Aurora borealis observed from Bossekop, Norway, on 9 January 1834. From Traité de l’électricité et du magnetisme (1840), by Antoine César Becquerel (1788–1878). Public Domain. Author’s copy.

Thales of Miletus (born c.626BC) a pre-Socratic philosopher, noted interesting properties of amber. Amber when rubbed would attract to itself certain light particles, and this fascinated natural philosophers for many centuries. Pliny the Elder (AD 23–79) and other writers also found that curative powers were bound up with electricity. One of the remedies in use among the Romans was the electric eel of the order Torpediniformes, which could be placed in a bath with a gouty patient (Figure 1.2). Pliny in his Natural History (Naturalis Historia) implies that it was well known as a therapeutic agent.³

FIGURE 1.2 Galvani’s spotted torpedo. From the Museum of Natural History (1860) by William Dallas. Public Domain. Author’s copy.

The 16th century can be viewed as the dawn of systematic knowledge of natural sciences, and the preeminent name is William Gilbert (1540–1603), Physician-in-Ordinary to Queen Elizabeth the First and President of the Royal College of Physicians. Gilbert first introduced the word electricity, while the appearance of his great work De Magnete in 1590 established the basis of electrical science.⁴ Gilbert’s major conclusion in his book, that magnets worked because the earth itself was a magnet, was a source of wonder to the readers of that day, who still, in the mood of the ancients, considered that such discoveries were direct emanations from a spiritual world. The sense of wonder does persist and for many the boundaries between physics and metaphysics are thin.

In 1643 in Italy, Evangelista Torricelli (1608–1647), a friend and pupil of Galileo Galilei (1564–1642), demonstrated the vacuum above a barometric column of mercury and paved the way for the introduction of the mercury pump. This observation led to the design of various forms of mercury pumps. Almost simultaneously, a German investigator, Otto von Guericke of Magdeburg (1602–1686), was conducting experiments in the hope of obtaining an empty space, in keeping with his theory that the stars maintained their motion by passing through such a negative atmosphere. He attempted to produce a vacuum by emptying a sealed water cask with the help of a piston water pump. Repeated failures led him to construct a mechanical air pump, which was similar to the instrument he had first used, while another of his devices was the first machine for generating frictional electricity. This invention, which was to have some significance for the production of a high-tension current, was a crude method for rubbing a rotating sulphur ball using the hand.

Some ten years later, the development of another pump, improving on von Guericke’s principle, was undertaken in about 1660 by Robert Boyle (1627–1691), who carried out experiments on the weight and spring of the air.

If mercury in a vacuum in a barometer is agitated in darkness, then flashes of light will be observed, and this was seen in 1675 by the French astronomer Jean Picard (1620–1682) as the phenomenon of barometric light. In 1705, Francis Hauksbee (1660–1713), who was Curator of Experiments to the Royal Society in London, was investigating mercury in a vacuum. Hauksbee described the phosphorescence of mercury globules, and did not initially see it as resulting from an electrical phenomenon.⁵ He developed his apparatus and used a spindle to rub one substance against another in an evacuated bell-jar (Figure 1.3). He was able to rub wool and amber beads together and again observed the pale light flashes. He repeated the experiment in the open air and noted “very little light did ensue in comparison to the appearance of it in vacuo”. He continued his work using a variety of materials, and when he used glass and wool, he saw a fine purple light when he rotated the spindle. This research carried out by Hauksbee is remarkable, and mark the earliest observation of the results associated with an electric discharge through a vacuum. Hauksbee’s work shows a definite commencement of what would become radiological research. The rubbing together of specific bodies is the oldest means of generating electricity, and Hauksbee’s purple light is a typical electric discharge, and was regularly seen by early radiologists when the gas X-ray tube had an incomplete vacuum. The next important date is 1729, when Stephen Gray (d.1736), who was a Charterhouse pensioner, demonstrated that some materials would conduct electrical properties for a distance and that some would not. Importantly, he showed that that metal wires conducted electricity.

FIGURE 1.3 Apparatus of Francis Hauksbee. From Hauksbee, 1709, see Note 5. Public Domain. Author’s copy.

Throughout the 18th century, the study of electric phenomena was popular in royal courts, including the French court. The leader was Abbé Nollet (1700–1770), who held the Chair of Physics at the College of Navarre and was Preceptor in Natural Philosophy to the Royal Family. His apparatus was his famous electric egg, which at the time was perhaps more an object of curiosity or parlour trick than being of scientific value. In the next century, its significance was appreciated.

The electric egg was a strongly made oval glass vessel, similar to an electric bulb, and when exhausted by an air pump and subjected to the transmission of an electric current produced by means of a frictional machine, it gave rise to a number of startling and colourful effects. These were not unlike the phenomena eventually produced in an X-ray tube of low vacuum. Nollet obtained his results by connecting his electrical generator to the electric egg by wires, which carried the discharges through the bulb (Figure 1.4). His observations were published in Paris in 1753.⁶ One day, out of curiosity, his fellow-worker, Charles François du Fay (1698–1739) suspended himself by a silken cord, and Nollet treated him to a charge of electricity from his frictional machine. He then touched du Fay’s hand, and a spark, as bright as it was surprising, was seen to pass between the two men. It was in 1734 that du Fay had noted that electricity was in two forms, which he called resinous and vitreous, now named as negative and positive terminals.

FIGURE 1.4 Abbé Nollet’s use of his electric egg. From Nollet, 1746, see Note 6. Public Domain. Author’s copy.

In 1745, Pieter van Musschenbroek (1692–1761) at the University of Leiden (Leyden) in the Netherlands developed the Leyden jar. The properties of this electrostatic condenser produced repercussions throughout Europe. The aim was to electrify water by rotating a glass bottle containing water and a central rod which was attached to an electrostatic generator. The Leyden jar is essentially a device to store static electricity and is a high-voltage device with a high-storage capability. A Leyden jar was sent to Benjamin Franklin (1706–1790), the American statesman and philosopher.⁷ By far, the best-known experiment in the development of static or high-tension electricity was that conducted by Franklin, and at that time only static electricity was known. His belief that the electricity of the earth and in the air were the same essential phenomenon was ridiculed, which Franklin overcame in his famous experiment. He made a silk kite which held an iron point. Fastened to the kite was a hemp string which, continuing as a silken cord, had an iron key attached to its end. The experiment was made in Philadelphia on a rainy day when Franklin released his curious apparatus in the wind. When it was made wet by the rain, the hemp string suddenly became a conductor, and Franklin then touched the key. A spark was immediately created, and this technique, by bringing lightning down to the earth, demonstrated its electrical nature at the same time as it proved his theory. Franklin noted that “thereby the Sameness of the Electric Matter with that of lightning is completely demonstrated”.⁸ Franklin also differentiated between positive and negative electricity, and between conductors and non-conductors of electricity, originating both terms.

Benjamin Franklin was resident in London and his house near Trafalgar Square, currently a museum, is his only surviving residence.⁹ During his time in London, Franklin met William Morgan (1750–1833). Franklin and Morgan both shared an interest in electricity, and were both sympathetic to the ideals of the French Revolution. William Morgan was a Welshman from Bridgend in Glamorgan, and was an apothecary and an early actuary.¹⁰ Morgan’s experiments were described in a paper read to the Royal Society of London on 24 February 1785.¹¹ Morgan’s experiments were carried out with a mercury gage, or evacuated glass tube, with a piece of tinfoil fastened at the closed end as a terminal. His purpose was to ascertain “the non-conducting power of a perfect vacuum”, which was a controversial topic. His paper implies that the various phenomena that accompanied an electric discharge through a vacuum tube were well known at that time.

In Morgan’s experiment, he found that by carefully boiling the mercury he obtained so high a vacuum that an electrical discharge was unable to overcome the high resistance of the tube. Morgan noted that the success of this depended upon the boiling, while on the least particle of air being admitted, an electric light, of the usual green colour, became visible. Under repeated charges, the tube at length cracked, when blue and purple colours were obtained. Morgan noted that if the mercury in the gage was imperfectly boiled, the experiment would not succeed; but the colour of the electric light which, in an air rarefied by an exhauster, is always violet or purple appears in this case to be of a beautiful green; and he further noted that, what is very curious, the degree of the air rarefaction may be nearly determined by this means. Morgan had known instances during his experiments when a small particle of air found its way into the tube, the electric light became visible, and was usually a green colour; but the charge being often repeated, the gage had at length cracked at its sealed end, and, in consequence, the external air being admitted into the inside had gradually produced a change in the electric light from green to blue, from blue to indigo, and so on to violet and purple till the medium had at last become so dense that it was no longer a conductor of electricity.

Now Morgan had inadvertently advanced beyond his object, which was only to demonstrate the non-conducting power of a barometric gage from which th...

Table of contents

• Cover
• Half-Title
• Title
• Copyright
• Contents
• Foreword
• Preface
• Acknowledgements
• Author Bio
• Chapter 1 Röntgen’s Discovery and Its Background
• Chapter 2 The Early Radiology Departments and the Problems They Faced
• Chapter 3 Radiology and Culture
• Chapter 4 Radiology and Anatomy
• Chapter 5 Dangers in the X-Ray Department
• Chapter 6 Tubes, Plates, and Screens
• Chapter 7 Radiologically Guided Intervention
• Chapter 8 Contrast Media
• Chapter 9 Radiology and Women
• Chapter 10 Tomography: Mechanical to Computed
• Chapter 11 NMR to MRI
• Chapter 12 The Future
• Index