Seeing the Invisible
Making the invisible visible, two young Canadians have developed an electron microscope which magnifies a grain of sand to the size of a 10-story building and penetrates a barrier which has baffled man since the beginning of time
ROYD E. BEAMISH
MATCHING strides with the most brilliant physicists in Europe, two young University of Toronto graduate students have developed, in the past eighteen months, a super-microscope of revolutionary importance to the world of science. And, as a result of their achievement, Albert Prebus, of Edmonton, Alberta, and James Hillier, of Brantford, Ontario, are sharing the thrill of exploration in a world never before seen by man.
This is a world beyond the range of light and shadow; a world whose largest object is smaller than the minutest organism ever seen before; and it is a world that may hold the answer to mysteries which science only yesterday believed incapable of solution.
The ordinary optical microscope magnifies an object to 1,500 times its actual size. Prebus and Hillier have already achieved magnifications of 30,000 times, and they believe that further development of their instrument will step its power up to 100,000 magnifications.
What this involves is best indicated by example. If a single grain of sand, measuring only one millimeter each way, were enlarged 30,000 times it would appear as large as a ten-story building standing on a base ninety-seven feet square. If it were enlarged 100,000 times, its dimensions would increase to 325 feet each way—in other words, it would be bigger than the Royal York Hotel in Toronto, largest hotel building in the British Empire!
This kind of wizardry is startling enough, but even more startling is the fact that the Prebus-Hillier microscope enables its operators literally to see the invisible. This they do by using an electrical ray instead of light to see with, an electrical ray so sensitive that it “sees” objects too small to be detected by ordinary light waves.
The instrument which possesses this phenomenal power stands in a brick-walled room of the McLennan Laboratory at the University of Toronto. A tubular structure, six feet in height, ruggedly built of heavy bronze, cast iron and copper, it bears scant resemblance to the optical microscope which is a familiar piece of laboratory equipment. If it were not for the imposing array of electrical apparatus surrounding it, the instrument might almost pass for the barrel of an overgrown machine gun, stood on end and supported by a four-legged stand that resembles a tripod.
Actually, it is a species of gun, for it fires a bombardment of electrons down the length of its four-inch barrel infinitely faster than any machine gun ever fired bullets.
It has been called, for want of a better name, an electron microscope.
“Seeing” With Electrons
IN USING electrons to see with, the new instrument harnesses the very essence of matter. Electrons are tiny particles, carrying a negative charge of electricity. They have been picturesquely described as “the building bricks of matter,” for the electron is one of the elementary units of all material substance—a component part of the atom, which is in turn a tiny part of the molecule.
Early in the twentieth century science learned that, under certain conditions, electrons can be torn from the atoms of which they form a part, and liberated in a stream. Any filament, heated with an electric current in a vacuum, for instance, gives off electrons. The filament of an ordinary electric light bulb is one example. The radio vacuum tube is another, though more complicated, electron producer.
Sir Joseph Thomson, master of Trinity College, Cambridge, first called electrons “negative corpuscles,” and established the fact that they carried a negative electrical charge. Later, his son, G. P. Thomson, and Louis de Broglie of France, found that a stream of these “corpuscles,” when concentrated into a narrow beam, acted in much the same manner as a beam of light; and it is from the discoveries of these three scientists that the development of the electron microscope owes its beginning.
In the early 1930’s, a group of German scientists, observing the similarity of behavior between light rays and streams of electrons, evolved an apparatus capable of producing controlled electron beams, passing them through an object, and transforming the beam into visible light by focusing it onto the same kind of screen that is used to detect X-rays.
This fluorescent screen, as it is called, was essential because electron beams have a wave length much too small to be detected by the human eye. Certain crystals, however, possess the power of absorbing these ultra-short waves and transforming them into light waves which are
visible; and so a screen, coated with these crystals, was placed in the path of the beam to record the image. loiter, the experimenters found that a photographic plate reacted to the electron rays in much the same manner as to light, and so permanent images were obtained by substituting the plate for the screen.
In 1934 the first German electron microscope had been developed to a state of practical efficiency, but beyond the unique substitution of electron beams for light rays as a source of illumination, it offered little to excite the imagination. The magnifying power of the instrument was no greater than that afforded by the standard optical microscope, and the resulting image was not always distinct.
Nevertheless, the degree of success attained spurred other physicists on in an effort to improve on the original.
A Belgian group, using the German apparatus as a model, constructed a similar instrument in 1935, but achieved no better results. Physicists in England also tackled the problem.
Hundreds of Experiments
JAMES HILLIER at the Uni 'ersity of Toronto, and Albert Prebus at the University of Alberta, as they pursued their studies, followed the progress of the European scientists closely. In 1937, after Hillier had graduated at
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the age of twenty-one, the two young men launched experiments of their own. Hillier remained at the university as a demonstrator in physics; and Prebus, three years his senior, arrived in Toronto from Alberta to continue post-graduate work on a studentship from the National Research Council of Canada.
They devoted every spare moment of their time to the laboratory, wrestling with the problem of creating a more efficient instrument. Literally hundreds of experiments were carried out, as new methods of overcoming technical difficulties suggested themselves. Dr. E. F. Burton, head of the Department of Physics at the university, shared their enthusiasm, and gave liberally of both time and advice as the instrument slowly evolved from the stage of vague theory to accomplished fact.
To the fundamental principles suggested by the first crude German instrument, the young Canadian scientists added refinements and alterations of their own design, and after more than a year and a half of patient progress by the tedious method of trial and error, their apparatus stood complete. Its builders plan to develop it still
further, but already it embraces refinements, magnifying power and delicacy of adjustment which are unique.
Already the two young scientists have mastered the technique of securing photographic record of objects magnified to 30,000 times their original size. And, as previously stated, when the full power of the instrument is engaged, they estimate the resulting magnification will be about 100,000 times.
While the two Canadians were developing their instrument, scientists in Berlin were conducting experiments based on the same broad principles. Although the two groups worked independently of each other, they had a common goal in sight, and the new German microscope, completed late last year, has paralleled the progress made in Canada. In one respect alone the Germans have gone farther, inasmuch as their electron microscope is already in commercial production. So far as scientific records show, no other nation has approached either Canada or Germany in the matter of the magnifying power of the apparatus.
XTOT since the seventeenth century, when the first crude optical microscope revealed the presence of living organisms infinitely smaller than the un-
aided human eye could see. has a single discovery offered the possibilities which science envisages in this new instrument. Apart entirely from the revolutionary principle involved in the substitution of electron rays for light rays, the electron microscope has torn down a barrier which has baffled mankind since the beginning of time.
In the past, despite improvements and refinements which slowly widened the field of the optical microscope, research workers knew there was a limit to the progress that could be made—a boundary beyond which man's ingenuity could not penetrate with light rays as his weapons.
That limit was fixed by laws of physics as immutable as the law of gravity itself. By mathematical calculation, physicists discovered that no object smaller than three-one-millionths of an inch could be seen by light. The shortest wave length of light was too great to record any object smaller than that, even when viewed under the most powerful lenses ever devised, and the limit of visual perception was reached with development of a microscope capable of magnification of 1,500 diameters.
To understand this more readily, we have only to realize that we see objects because they interfere in some manner with the passage of a wave of light. If they are so small that the light can pass through or around them, they are invisible, for what we see is only the amount of disturbance or diffusion created in the light waves on their way from their source to our eye.
Waves on a lake will illustrate the point. Imagine a small boat out on a lake in a storm. The boat will not interfere much with the passage of the big waves blown up by the storm. It is as rough on one side of the boat as on the other. But when the waves reach a high sea wall, they are turned back or interrupted momentarily at least. If two objects of sizes proportionate to the boat and the sea wall were in the path of a light wave, the one corresponding to the sea wall would be visible; the other would not.
But, supposing the same boat is out on the lake when only a light breeze is blowing and tiny ripples are being stirred up. Their wave length—the distance from crest to crest—is much smaller. On the windward side of the boat they are advancing just as would the big waves in a storm. But they are so much smaller than the boat that they are interrupted by it, and the leeward side is calm for a few feet before the ripples regain their normal course. Under such circumstances, the “boat” would be visible.
It is true that objects invisible to the naked eye can be seen through a microscope, but this does not in any way contradict the rule just stated. All the microscope does is concentrate the illumination upon the particular object by gathering more light and bringing it to the eye. If the object is smaller than the wave length of light, no amount of optical magnification will reveal it.
Like light, electrons exhibit the properties of waves, and objects placed in the path of an electron beam disturb the passage of these waves. Like light, also, electron waves leave a visual impression, or silhouette, of objects they encounter, if they are focused on a fluorescent screen. But their wave length is about one thousand times smaller than the wave length of light, and can be made smaller still under pro|>er control. Which means that, theoretically at least, the limit of the smallness of objects which can be “seen” by the electron wave can be extended indefinitely—provided, of course, you can persuade the electrons to register what they “see” in a manner decipherable by the human eye.
IT WAS on the basis of these known facts that Prebus and Hillier began construction of their weird instrument.
Production of the electrons was a simple matter, a tungsten filament in a vacuum and an electric current to heat it being the only requirements, but an intricate engineering technique was involved in the control of the electrons and the assurance of a constant wave length, so that the resulting image would be clear and distinct. The faster electrons travel, the shorter is their wave length, and the velocity of the electrons had to be kept absolutely constant to assure uniformity. Any fluctuation resulted in a blurred and distorted image.
It was also necessary to find some means of forcing the streams of electrons into a single beam, so that the energy could be directed along a clearly defined, prearranged path from its source to its eventual destination.
A single device overcame both difficulties. A small metal plate, with a tiny hole in its centre, was suspended in the tube of the instrument a short distance below the end of the filament, and connected to the ground. When a high voltage was applied between the heated filament and the metal plate, the electrons released from the filament were forced through the small aperture at an enormously high velocity, and continued on their way in the form of a narrow beam. The velocity of the beam was controlled by varying this high voltage. At the time of writing, the instrument was being operated at 45.000 volts.
An elaborate battery of condensers and other equipment was required to keep the voltage constant, and control of the power supply is one of the most important fundamentals of the instrument's operation. A description of the control system would involve a highly technical explanation, but suffice to say that it has been developed to the point where it will maintain a voltage constant to within one volt in 45,000.
A great deal of the time and about ninety per cent of the money spent on the building of the apparatus were devoted to this power-control system; and in the process two costly condensers’ were placed at the disposal of the University of Toronto by the University of Alberta.
Photographing the Invisible
ANOTHER major difficulty was the perfecting of the means of collecting and concentrating the resulting electron beam in order to produce high magnifications. In the optical microscope, glass lenses are used to bend and gather light, but electron waves will not pass through glass.
Earlier experiments had shown that electron waves could be deflected from their course by placing a magnet near them, and this principle was applied to the devising of lenses for the new instrument.
The physicists simply surrounded the beam with a magnetic “collar”—a tightly wound coil of fine copper wire, magnetized by an electric current—which focused the electron beam in much the same way that a glass lens focuses light. Three such “magnetic lenses” are used in the Toronto instrument.
The amount of current flowing in the electromagnets determines their magnetic force, and the stronger the magnet, the greater effect it has on the electrons passing through, so focusing is controlled by increasing or decreasing the strength of the current with a simple rheostat The image is brought out to its desired sharpness by simply moving an indicator until the exact strength of current required has been obtained.
Setting up an object for study under the new microscope is an extremely delicate task, partly because the object is microscopic in size to begin with, and partly because the terrific magnification requires the utmost accuracy.
A thin platinum disc, with a hole in the centre smaller than the point of a fine needle, replaces the customary glass slide for the “mounting” of a specimen. The object to be studied is floated on a thin film of collodion, and then manipulated over the tiny opening under an ordinary microscope. Two hours or more are often required to complete this delicate operation. When it is in position, the platinum disc is carefully mounted in the path of the beam in the electron microscope.
In operation, a high vacuum is created in the instrument by pumping out the air with a mercury pump. This is essential, for, just as in the case of a radio tube, the electron stream functions only in a vacuum.
The filament is then brought to a white heat, the high voltage switched on, and the microscope is ready for use. The 45,000 volts between the heated filament and the metal plate below, accelerate millions of electrons to a terrific speed. Most of the electrons are stopped by the plate, but some of them hurtle through the tiny aperture in its centre, whence they emerge as the beam which “sees” the invisible.
A magnetic lens focuses the beam to a pin point directly over the object, which is firmly held in a brass saddle. A short distance beyond, the beam passes through another lens, and falls on a fluorescent screen, to produce a pale green image of the original object, magnified some 200 times its actual size. The screen, pierced through its centre with a single tiny hole, is movable, and the operator merely selects the portion of the image which he wishes to study in greater detail, and manipulates the screen so that the aperture comes directly under the part selected.
The electrons which have “seen” the corresponding portion of the original object, thus pass through the tiny aperture to continue their journey down the six-foot tube, while the others are held back by the fluorescent screen. Again the beam passes through a magnetic lens for further magnification, and again it falls on a fluorescent screen, and this time the image is magnified 200 x 200 times, to produce a magnification of 40,000. When the image has been accurately focused, the screen is withdrawn and the rays permitted to fall on a photo-
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graphic plate, which records the picture permanently.
SOME OF the photographs recorded in the Toronto laboratory are reproduced elsewhere in these pages, and they offer eloquent proof of the instrument’s power. One shows the cutting edge of a small portion of a safety razor blade, one six-thousandth of an inch in length, magnified 30,000 times. Although the razor edge has been sharpened to the keenest degree possible by the most modern precision machinery, the electron microscope pictures it as a jagged ridge.
The practical value of the instrument has already been demonstrated. In one instance, a Canadian oil company, which utilizes a particularly fine type of clay for the purification of oil, was unable to discover why the clay was useless for this purpose after it had once been used. The clay was burnt after use to drive out the impurities, and the burnt clay no longer functioned as a filter. Examination of clay particles under an optical microscope revealed no difference in their consistency before and after burning, and company officials were frankly puzzled. The electron microscope answered the question. Under its high magnification, particles of clay were examined. The instrument showed that the unused clay had an irregular, jagged surface, indicating the presence of pores or pockets which evidently trapped impurities in the oil; while the used, burnt clay was relatively as smooth as a billiard ball, having lost its absorbent quality in the burning. Electronic pictures of the two specimens show this difference clearly.
The scientists are chary about discussing the future possibilities of the new microscope, but they will admit that it has enormously extended the horizon in fields of research which still hold many mysteries. One of the most important of these is the field of bacteriology. Heretofore, the study of disease-bearing organisms has been handicapped by the fact that some of our most devastating diseases are caused by viruses too small to be seen with the optical microscope. Diseases such as smallpox, scarlet fever, measles, poliomyelitis and rabies are among many believed to be caused by viruses which fall into this category.
At magnifications over 10,000 times, however, there is definite possibility that these invisible viruses will be revealed— which would be a long step toward con; quest of the diseases they cause. For that I reason, study of these heretofore invisible i viruses will be one of the major applications of the new instrument.
The search for viruses, however, is but one of a multitude of fascinating problems awaiting investigation by the amazing new device. In theory, at least, it has opened up a field of view which extends down to the size of the atom. The 45.000volt beam used in its operation today has made objects visible far below the range of light. Use of still higher voltages will increase that range proportionately by giving the electron waves still smaller wave lengths. Chief difficulties lie in the perfecting of the lenses, and in the developing of the highly specialized and costly electrical equipment necessary to produce the high voltages required and maintain them at a constant level. Upon the solution of these difficulties depends the development of the new instrument to the point where it will make possible the study of the ultimate constitution of matter itself.
“The Hard Way”
SO MUCH for the instrument. What of the men who built it?
In the light of the importance of their achievement, perhaps the most striking thing about them is their youth. Prebus, tall, fair-haired, with high forehead and ascetic, lean features, looks the part of the mature student. He is twenty-siv. Hillier, only twenty-three, looks more like a school-
Each has achieved scholastic success the hard way. Prebus was born on a farm near Edmonton, of German parents who came to Canada forty-one years ago. His early life was that of the typical Western farm boy. Hillier comes from a modest Brantford family of British stock, with just a trace of French in his ancestry. Both have had to scratch for a living.
Both boys hurdled the financial barrier to a college education by winning matriculation scholarships which carried them into universities, with tuition fees paid—Prebus at Alberta, Hillier at Toronto. Part-time work during the school terms, full-time jobs during the summers—Hillier was a grocery clerk one summer—and additional scholarships won from year to year, kept them at college. Both now have their master’s degrees.
Coincidence played its part in their becoming partners in scientific adventure. Independently, they each chose electron optics as their field of post-graduate research—the only two students in Canada to make that choice. That being so, when Prebus arrived in Toronto, he was allocated to the same laboratory as Hillier, so that the two might work together. And, to this fact, both young men attribute the construction of the electron microscope.
“I had no intention of going into that phase of electron optics,” Hillier explains. “It was too big a job for any man to tackle alone. If we both hadn’t got the same idea at the same time, I don’t think either of us would ever have attempted it.”
Actual construction of the instrument was carried through in the face of limited finances, and the budget available for research projects made no allowance for an undertaking of such major proportions, and there were insufficient funds to purchase the highly specialized precision equipment required.
The two adventurers became their own machinists, fashioning each intricate part of their apparatus slowly and painstakingly in the Physics Department m chine shop. Their instrument as it now stands is literally a homemade job, completed at a cost of approximately one tenth the quoted price of the German apparatus.
The mere business of living also presented financial difficulties. Both are married, and one has a child. Hillier, as a demonstrator in the physics department of the university, is paid $1,100 a year. For this he teaches full time during the academic year, and much of his contribution to the building of the microscope had to be made at night. Prebus has had an income of $650 for eight months of the year from the National Research Council of Canada, supplemented by a small weekly payment during the summer months.
As might be suspected, neither is much interested in luxury or wealth. Their chief ambition is to improve their instrument and develop its applications. They have said flatly that, so long as they can earn enough to maintain a reasonable standard of living for themselves and their wives, nothing will lure them away from their chosen field of research.
‘‘There’s a lifetime of work ahead of us in that microscope,” Hillier says, ‘‘and I’d hate to give it up now that we have just nicely started. But we do need money to develop it further—money to develop the instrument itself, money to carry on intensive research in fields in which it can be usefully applied.”
Ten thousand dollars a year would probably finance an adequate program. In relation to the literally incalculable potentialities of the new instrument for extending man’s knowledge, the amount is insignificant.
Among physicists Prebus and Hillier will be world famous when the story of their achievement is published in the scientific journals. Their services will be in demand. Whether those services will be retained for Canada remains for Canadians to say.