"The idea of doing this experiment came to me one morning while I was shaving. I noticed that the capillaries in the white of my eye are covered with transparent tissue, and I wondered what the blood would look like if I could see it up close. The question itself suggested the kind of instrument I would need: an optically folded microscope. Light from the capillaries of one eye would pass through the objective lens of a microscope and proceed to a distant mirror for reflection to the other eye [Figure 1]. I had a 10-power objective lens and a 10-power eyepiece. Luckily I also had a small mirror that was silvered on the front side. Mirrors silvered on the back would not work as well because light would be reflected from both the front and the back to create a double image.

"Experimenting with the apparatus, I soon learned that all parts of the system, including the viewer's head, must be rigidly supported because all motions of any part are equally magnified. In my design the objective lens, the eyepiece and the mirror are supported by a wooden box. The box rests on and is attached to the upper end of a lens barrel from an old portrait camera. The barrel has a rack and pinion that serve as a focusing adjustment. The framework holding the lens barrel is made of wood and includes both a head board and a bite board [see Figure 2 ]. These rests are essential. Indeed, I have been tempted at times to strap my skull to the fixture.

"Neither the dimensions nor the arrangement of the parts is critical. The experimenter can be guided by the contents of his junk collection. Focusing can be accomplished by moving the entire optical system up or down, as in my design, or by moving the objective lens alone. I light the capillaries with a spot lamp that I made, and regulate the brightness with a rheostat. I always use minimum light to prevent irritation or damage to the eye, and I usually limit periods of observation to five minutes, with an hour or two of rest between periods.

"What does one see? This depends on the size of the capillaries. I classify the capillaries simply as large, medium and small. The large ones show no flow of blood because the stream is thick and consequently opaque, nor is regular flow observed in the smallest capillaries. Single cells or small clusters of cells spurt irregularly through the smallest capillaries much as random tracks appear in a Wilson cloud chamber. The most interesting flows are found in capillaries of medium size, which are both clearly transparent and supplied with just enough blood to display the streaming red cells to advantage.

"I found viewing my own blood a fascinating experience. Here and there the cells move in synchronism with the pulse, alternately speeding up and slowing down, but the action of the heart is not apparent in all capillaries. In man the flow is constant. Occasionally the blood comes to a complete halt and then resumes in the same direction. Most astonishing are times when the cells stop and reverse direction against the powerful pumping of the heart. Another stop follows, and then the flow resumes in the original direction. Rarest of all are occasions when a capillary empties. This usually occurs during a backflow, when for some reason the blood supply appears to be cut off. The capillary seems to vanish, but it reappears in a matter of seconds with the return of normal circulation.

"Several experiments come to mind. For example, it might be interesting to observe the effects of coffee, tea, beer or tobacco on the circulation. It should also be possible to investigate the influence of aging on the structure of certain capillaries and on the circulation. Such changes could be photographed by fitting the eyepiece with an optical beam splitter to divert part of the light into a camera. The apparatus would similarly lend itself to recording the effects of emotional or mental states on the circulatory system."

The next project is submitted by Cleveland H. Hood of Middlesbrough in England, who makes a hobby of constructing meteorological instruments He calls attention to an inexpensive device for electrically synchronizing the rotary motion of two mechanically independent shafts. The device consists of two principal assemblies: a transmitter and a receiver.

The transmitter includes a rotatable shaft that carries two electrically insulated wiper arms spaced 180 angular degrees apart. The tips of the arms make sliding contact with a surrounding toroidal coil of resistance wire. A comparable shaft of the receiver supports a bar magnet, much like the needle of a compass, that is free to rotate inside a surrounding configuration of three interconnected solenoids spaced 120 angular degrees apart. Direct current is applied to the wiper arms. From three points spaced120 angular degrees apart on the toroidal coil leads connect to each of the corresponding solenoids [see above left].

When power is applied to the transmitter, the resulting current divides into three parts. The amount and the relative polarity of each part depend on the points where the wiper arms make contact with the toroidal coil. These currents induce a corresponding pattern of magnetic flux in the region of space enclosed by the solenoids. The bar magnet aligns itself with this field. Rotation of the transmitter shaft redistributes the current and, in effect, rotates the magnetic field of the receiver. The bar magnet and its supporting shaft turn in step.

Hood writes: "Any reasonably handy craftsman can construct a version of this synchronizing device, but in Britain (and perhaps in the U.S.) the transmitter and receiver are available on the surplus market. Known as the 'Desynn System of Remote Indication,' they are manufactured for use with airplane instruments by Smiths Industries Limited, Kelvin House, Wembley, Middlesex, England.

"I picked up a set of Desynns in the surplus market for 16 shillings (about $2) for remote display of wind direction at my home weather station. The weather vane is on high ground some distance from the house. The lower end of the vertical spindle that supports the vane assembly is coupled to the Desynn transmitter. The receiver of the Desynn displays on a dial in my study the direction in which the distant vane is pointed.

"The design of the vane is novel in that the moving parts float in a container of light machine oil. The spindle passes through and is soldered to the axis of a sealed cylindrical can that functions as a float [see above right]. The oil that supports the float is contained by a glass jar that also serves as the base of the instrument.

"I wedged the Desynn transmitter in the bottom of the jar and joined its shaft by a spline to the lower end of the spindle. A sleeve bearing in the lid of the jar supports the spindle vertically. The perforated lid of a round tin can was soldered to the spindle just above the sleeve bearing to act as a rain shield. The spindle attaches to the balance point of the horizontal arm that carries the vane.

"The buoyancy of the float was adjusted, by putting oil inside, to counterbalance the weight of the rotating assembly. The weather vane behaves as though it were weightless and nearly frictionless, as indicated by the fact that it responds to an almost imperceptible breeze. It has operated continuously without maintenance in weather of all kinds for more than a year."

A discouraging phenomenon tends to beset those who first attempt to grind and polish the objective mirror for a reflecting telescope. At least one deep scratch mysteriously appears in the glass no matter how carefully the craftsman works. Telescope mirrors are ground to a concave figure by sandwiching an abrasive slurry between two disks of glass and pushing the top disk back and forth. As the grinding proceeds the lower surface of the top disk, which will function as the mirror, becomes increasingly concave and the top surface of the lower disk, which acts as the grinding tool, becomes correspondingly convex.

The worker uses successively fine particles of abrasive and finally polishes the lightly frosted surface of the mirror to a paraboloidal figure by stroking the glass on a disk of pitch coated with a slurry of rouge. All instruction books admonish the beginner to use abrasives of high quality and to maintain scrupulous cleanliness in order to prevent a coarse particle of grit or dust from lodging between the disks and making the unwanted scratch. Although scratches have almost no effect on the optical performance of the telescope, they are irksome to craftsmen who prize excellence in workmanship. T. R. Macfarlane of Regina, Saskatchewan, describes a little-known but reliable method of ending the difficulty:

"Scratches are made by lumps that form in all grades of fine abrasive. The lumps plow grooves in the glass just as though they were solid particles. They can be dispersed by a sedimentation procedure that improves the abrasive in another respect. All grades of abrasive contain powdered grit: particles much smaller than those of the maximum size. When the powder becomes wet, it acts like mud in that it retards cutting action. By removing the powder the time required for the final stages of grinding can be cut in half.

"Abrasives are graded by number, ranging from 80 (particles about the size of granulated sugar) to 600 (microscopic particles). The coarser grades do not clump and rarely cause scratches. The difficulty appears with grade 320 and smaller. To purify abrasives you will need a few jars of clear glass ranging in size from a quart to a gallon, small jars with caps to hold the purified abrasive, four feet of rubber hose a quarter of an inch in diameter and a quart of water glass (sodium silicate).

"I put clean water, to which I have added about two ounces of water glass, in a gallon jar until the level is an inch below the top. The water glass serves as a deflocculating agent: it disperses lumps that remain solid in water alone. One ounce of abrasive is thoroughly mixed with the solution and left to settle for 30 minutes. With the rubber tubing I then siphon all but two inches of the fluid into a clean container. I label the container 600-1 and put it aside.

"I refill the settling jar with water containing one ounce of water glass, thoroughly mix the remaining grit and again let it settle for 30 minutes. All but an inch of the fluid is then siphoned into a clear glass container and labeled 600-2. Thereafter I repeat the procedure, progressively reducing the intervals of settling to 15, eight and three minutes. The stored containers are labeled 600-3, 600-4 and 600-5 respectively.

"Finally, I shake up the settled dregs and pour them into a smaller jar. This material settles quickly. A sharp line appears at the boundary between the clear fluid and the suspended grit. When the upper third of the fluid clears, I carefully pour all but a third of the remainder into a clean jar. When this material settles, I pour off and discard the clear fluid. I then refill the jar that contains the dregs and repeat the procedure three times. The collected material is labeled 600-6. To the remaining dregs I add one ounce of the 600 grit as it comes from the manufacturer, process it by the same procedure and similarly treat the remaining stock. After several days, when the grit in all six labeled containers has settled, I carefully siphon off the clear fluid and dry the abrasives for use.

"What about the accumulated dregs? To them I add one ounce of 500 grit, proceed as described and then switch to 400, followed by 320. I do not process the coarser grades.

"Purified abrasive easily cuts twice as fast as untreated material. During the final grinding stage, when 600-6 grit is followed by 600-5, -4, -3, -2 and -1, the glass emerges unscratched and with a semipolished surface. Other deflocculating agents and techniques of sedimentation that differ slightly from this procedure are described in Amateur Telescope Making (Book Three), by Albert G. Ingalls (Scientific American, Inc.)."

Occasionally an unexpected event such as the flick of a pointer across a dial, a puff of smoke or a flash of light alerts the careful experimenter to a fruitful opportunity. A case in point is reported by W. W. Withrow of Teague, Tex., who recently hit on an inexpensive method of measuring the electrical conductivity of materials ordinarily classed as insulators. He writes as follows:

"Some months ago I received a number of transistors from a cousin who works for a computer manufacturer. The devices had been rejected during tests at the plant. They were designed to conduct current from the emitter to the collector terminals but not in the reverse direction. I decided to measure their resistance in the reverse direction, on the assumption that those of high resistance might be usable. The measurements were made with an inexpensive ohmmeter that has a midrange scale of 150,000 ohms.

"During all the tests except one the pointer of the meter swung to the top of the scale and stayed there, indicating a usable transistor. In this one case, however, the pointer first swung to the top of the scale, flickered a few times and finally dropped close to zero. Initially I thought the device was defective. Then I became aware that the tip of one of my fingers was touching both the collector and the base terminals of the transistor. When I removed the finger, the pointer swung to the top of the scale, as in the case of units previously tested. Evidently current through my finger was triggering the transistor into its amplifying state. The relatively small current in the base-collector circuit caused a large current in the emitter-collector circuit. It occurred to me that the transistor might be used to magnify the scale of my ohmmeter, perhaps from its normal midrange of 150,000 ohms to several million ohms.

"To test this notion I clipped the positive terminal of the meter to the emitter lead of the transistor and the negative lead of the meter to the collector. (The silicon transistor was of the p-n-p, or positive-negative-positive, type.) I then connected a one-megohm resistor across the collector and base terminals of the transistor. The pointer of the meter promptly swung to 10,000 ohms, which suggested that the transistor had magnified the scale of the instrument 100 times, equivalent to a midrange value of roughly 15 megohms. The thing had workedl

"Why not place another transistor ahead of the first one and get still more magnification? This was done by connecting the base of the first transistor to the emitter of the second one and interconnecting the collector leads. In this circuit the transistors function as a two-stage current amplifier [see illustration below]. The circuit again worked, amplifying 10,000 times to yield a midrange scale of 1,500 megohms.

"Rough measurements are of little use. My next step was to calibrate the magnified scale, which can be done with two resistors, one having a known, fixed value and the other being variable from zero to at least 1,500 megohms. The resistor of known value is connected in series with the variable resistor. The variable resistor is set to zero and the fixed resistor alone is measured. The position to which the pointer swings is noted. The fixed resistor is short-circuited by connecting a copper wire across its terminals. The variable resistor is adjusted so that the pointer swings to the previously noted position. With the pointer at this position the value of the variable resistor matches that of the fixed resistor.

"The value of the fixed resistor can now be added to the circuit by removing the copper wire. The pointer then swings to a new position that is equal to twice the value of the fixed resistor. With the fixed resistor again short-circuited the variable resistor is adjusted so that the pointer swings to the new position on the scale. The cycle of operations is repeated until the expanded scale is fully calibrated.

"Fixed resistors calibrated to within 1 percent of their rated value are available from suppliers in sizes up to several megohms. Obtaining a variable resistor of the size needed for this job is another matter. Variable resistors of zero to 3,000 megahms are not available commercially. I tried a number of ways to improvise one with several materials in my shop.

"One of my devices seemed promising. It was a wood scrap two inches wide and two feet long with a series of steel nails driven in a row down the middle to serve as terminals. The strip had about the right order of conductance, but the conductivity changed faster than I could clip instrument leads to the nails. Evidently current in the wood was carried by absorbed moisture.

"After trying a number of other materials without success I finally hit on the idea of using a cadmium sulfide photocell as a light-dependent resistor. I sealed the photocell in a small, lightproof box along with a miniature lamp bulb, a flashlight battery and a rheostat for adjusting the brightness of the lamp with a knob outside the box [see illustration above]. The maximum resistance of the cell in darkness is about 3,000 megohms. All photocells of this type are sluggish: their resistance continues to change for several seconds after each adjustment of the light. Their resistance also changes with temperature and other variables. Even so, if one is patient, the device can be used to calibrate the ohmmeter. Any type of silicon transistor with a current gain (beta) of 100 or more will work in the ohmmeter circuit.

"Resistances up to a billion ohms are normally measured with a 'megger,' essentially a hand-cranked generator, that develops several hundred volts. It is connected to a meter that responds to a few millionths of an ampere. Meggers are costly and inconvenient to use. The same measurements can be made by fitting a $20 ohmmeter with a pair of silicon transistors. I use mine for checking capacitors, insulators and similar electronic components."

Bibliography

FUNDAMENTALS OF OPTICS. Francis A. Jenkins and Harvey E. White. McGraw-Hill Book Company, Inc., 1950.

AMATEUR TELESCOPE MAKING (BOOK THREE). Edited by Albert G. Ingalls. Scientific American, Inc., 1953.

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