THE U. S. CLIMATE tends to reach its extremes in the nation's four corners. Wynoochee Oxbow, Wash., is the wettest locality: during one 13-year period annual rainfall there averaged about 150.73 inches. The most violent downpour, however, was recorded in the Southwest at Thrall, Tex., where during a 24-hour interval on September 9, 1921, a rain gauge measured 38.20 inches. The southeast corner of the nation claims the second heaviest rain: 23.22 inches during a 24-hour period in October, 1924, at Smyrna, Fla. Greenland Ranch in Death Valley, Calif., records the smallest rainfall: a yearly average of only 1.35 inches. Greenland Ranch also claims the temperature high, 134 degrees registered on July 10, 1913. The record low is 66 below zero, observed in Yellowstone National Park on February 9, 1933. From the remaining corner, the state of Maine insists that a snowfall of 96 inches in four days puts her in competition with California's 884 inches-more than 73 feet-during the winter of 1906-07. The best that the central states can do is to claim a record for the largest hailstone ever measured: a stone which fell at Potter, Neb., on July 6, 1928, and, placed on the scales immediately, weighed 1-1/2 pounds!

All of these statistics, together with unnumbered millions of others, were gathered by members of an organization of amateur weather men who cooperate with the U. S. Weather Bureau. Officially they are known as Cooperative Weather Observers. Their geographic distribution across the nation is indicated by the map on page 115. No matter where you go in the U. S. you can find an amateur meteorologist within 50 miles, and the chances are not remote that one lives across the street from you. Most of these amateurs are cooperative observers for the Weather Bureau.

These amateurs play a direct role in all our lives. They contribute to our comfort and stretch the pennies in .our pocketbooks. The price of fuel oil for space heating, for example, is largely determined by the cost of local distribution. If your fuel dealer can hold down the frequency of his deliveries by making maximum use of the storage capacity of your tank, he can reduce his bill. If you are willing to cooperate, the dealer will permit the pattern of your local climate to dictate your delivery schedule. In the U. S. that pattern is charted almost solely from data contributed by the Cooperative Weather Observers. What you will pay for coffee a year from now can be estimated from their reports. These observers also play a military role. Should the date for testing a guided missile at White Sands proving ground in New Mexico be set for October 15 or November 15? The probability of the desired weather on each date can be ascertained by Army meteorologists in a few minutes -from records compiled through the years by cooperative observers. On which side of Indianapolis, Ind., should you erect a new factory for, say, making fine electrical instruments? Where in the U. S. would breadfruit thrive? Should your daughter plan to hold her garden party early or late in June? Collectively the cooperative records can give you climatic odds to meet any of these needs, along with a factor of probable error that is exquisite in its refinement.

Like amateur groups in general, cooperative observers come from all walks of life. The first weather records on the American continent, according to W. F. McDonald, Chief Climatologist of the U. S. Weather Bureau, were kept by the Reverend John Campanius at Swedes Fort near Wilmington, Del., in 1644. It was not, however, until 1891, nearly 250 years later, that the immensely valuable work of the amateur weather observers came in for official recognition. The present dean of the observers is Dudley I. Craig, a civil engineer who lives on the Pinal Ranch in Arizona. Mr. Craig became a cooperative observer on March 1, 189S, at the age of 18 There is no adequate measure of the service he has freely contributed to his fellow citizens. His record spans more than 60 years.

At the other age extreme we find the granddaughter of Charles F. Brooks, Director of the Blue Hill Observatory of Harvard University, who became an assistant cooperative observer at her home in Missouri at the age of six. Her admission to the ranks illustrates the fact that sometimes whole families get into the act. All seven of Dr. Brooks' children are interested in weather observation and forecasting-one of them professionally. It is not at all uncommon for a son to continue records first kept by his father. Hundreds of the thermometers and rain gauges that the Weather Bureau has issued to amateurs over the years are now being tended by the third generation.

Few amateurs in science can compete with the weather men and women in regularity and devotion. Hundreds of them have been reading their "max-min" thermometers seven days a week at precisely the same time each day, 7 a.m. or 7 p.m., for more than a decade at the same address without a single miss! Some have done so for more than 50 years.

Offhand it may seem that keeping track of the weather and making studies of local climate can scarcely provide enough activity for a full-scale avocation. To learn what keeps an amateur meteorologist busy, we dropped in on William Martin recently. His weather station at Long Branch, N. J., has earned a Class B rating, which means that he is authorized to disseminate official Weather Bureau forecasts for his community. Mr. Martin works for the telephone company and lives in a large, two-story house in a quiet part of town.

We asked him how an amateur meteorologist spends his day. "It begins at 5:30 a.m.," he said, "and often fishing crews begin calling even earlier. I don't have much time for breakfast, because the recording instruments have to be serviced, and two of them, the water thermograph and wave recorder, are located on the beach more than a mile away. They show the temperature of the ocean and how rough it is. Often I have to make a special trip to the pier to fly storm warnings. When these jobs are out of the way and all the readings are in hand, I call New York. We have a direct wire to the Weather Bureau office there and I usually spend half an hour or so exchanging data. Then I get busy on the paper work. Meanwhile Mrs. Martin handles the incoming calls. We have two telephones and average about 50 inquiries a day. During hurricane weather the calls go up to 400 or more. When the records are finished, it's time for me to get down to the local broadcasting station, where I go on the air with the weather at 7:30. After the broadcast it's time for work. We amateurs have to earn a living the same as anybody. The evening routine is pretty much the same, except that other chores substitute for the charts and broadcast. We have quite a few instruments to maintain, and that means an endless round of tinkering."

Martin's instruments are installed all over the place. Several were supplied by the government. A 65-foot tower near his garage supports a recording air vane, two anemometers-one for measuring wind speeds down to one mile per hour and the other for gusts of hurricane intensity and an ultra-high-frequency radio antenna. Two rain gauges, one an automatic dump-bucket type which registers inches of rainfall on a graph in the house, are installed in his back yard at a spot protected from the wind. Behind the garage a 14-foot tower supports a small, ventilated enclosure reached by a stairway. This is the instrument shelter. It is made of slats, somewhat like a Venetian blind, which permit a free circulation of air. It houses conventional minimum and maximum thermometers, a barograph, a thermograph, a hair hydrograph, wet- and dry-bulb thermometers and a thermocouple which works with a remote dial in the house for convenience in reading outdoor temperature. The sensing element of a sun gauge is mounted on the roof of the house and registers on a graph indoors.

A converted bedroom on the second floor serves as the operating center of the station. Two sides of the room are taken up by instrument panels. All over the room is a clutter of cloud charts, weather maps and related tabular displays such as you would find in a Weather Bureau office.

"Not much activity tonight," observed Mr. Martin. "We will have nice weather today and tomorrow. There's a big high moving in slowly from the midwest and another off Bermuda. You've probably heard about Barbara. That's the name of 10 the season's second hurricane. She's about 300 miles east of the Florida coast right now and moving north at eight miles per hour."

At that moment the telephone rang and Mrs. Martin told a local yachtsman that it would be all right for him to take a cruise off the Jersey coast the following day. "If the pattern of highs fails to move as it should," Martin continued, "Barbara can give us some nasty weather. But she will need at least three days to reach here, When hurricanes threaten, we get a lot of calls like the one Mrs. Martin just answered. You should come down the day after tomorrow if you want to see how things go when we get busy."

We asked Mr. Martin what he finds most interesting in his hobby. "I enjoy reading about the scientific aspects of weather a lot," he said, "but I rely on the Weather Bureau for technical information. Some of the other fellows, like Harry Larkin, who keeps a station at Elma, N. Y., or Wendell Kilmer, out on Long Island, go in for meteorological research. I specialize more in the application of weather information."

Martin's reference to Harry Larkin reminded us of our visit to Elma some months ago when Larkin described his seismological station for this department. Larkin's interest centers principally in the dynamic processes of weather. As his account in our April, 1952, issue remarked, he is concerned with the relation between the movement of low-pressure regions in the atmosphere and the intensity of microseisms in the earth.

FOR several years Larkin has also been investigating the theory of pre-frontal waves. According to this theory, the violent interaction of two air masses can generate waves of pressure which are propagated a considerable distance, as much as 150 miles, in advance of the front. Such waves, appearing without warning, may explain why aircraft sometimes get into trouble while passing through zones thought to be free of dangerous turbulence. If such pre-frontal waves exist, Larkin reasoned, under appropriate meteorological conditions thin clouds should form in the low-pressure regions of the waves and disclose their presence. To check the theory Larkin set up a horizon-to-horizon motion picture camera which makes time-lapse photographs of the sky every day from dawn until dusk. The results, although incomplete at present, have attracted wide attention in professional meteorological circles.

The theory of pre-frontal waves is only one of a great number of meteorological problems open to study by amateurs. The field of micrometeorology, for example, offers almost endless opportunity. Several years ago amateurs in a section of Long Island, among them Kilmer, who is a professional photographer, noticed a curious disagreement of their early-morning temperature readings. The thermometers in a narrow region near Kilmer's station read some 20 degrees lower than those in the surrounding countryside. From this accidental observation grew a study which took many months. More than a score of amateurs cooperated in establishing a fine-grained network of observing stations in this area, and in this way they discovered and mapped Long Island's famous "ice box."

The ice box occupies an elongated depression in the vicinity of the Brookhaven National Laboratory. It lies between two low ridges that shield it from heat radiated by Long Island Sound on one side and from the Atlantic Ocean on the other. A narrow valley links it with the sea. Its soil consists, for the most part of light-colored sand.

By making many closely spaced observations of temperature and wind direction near the surface, the amateurs gradually learned what makes the ice box work. The explanation begins with the fact that heat is radiated from the sand more readily than from the soil of the surrounding terrain. When the sun goes down, this cooling creates a layer of dense air over the area. The cool air then flows down to the sea. Thermometers begin to drop. Cool air forming over the surrounding terrain also is drawn into the ice box and flows to the sea. The ice box thus becomes a meteorological drainage area. In the meantime the surrounding terrain is absorbing heat radiated from the Sound and the Ocean. Hence the temperature differential continues to increase, with the coldest air always flowing into the drainage system. From a practical point of view your appreciation of the ice box will depend on whether you are a truck farmer intent on raising late tomatoes in it or an office worker seeking a dwelling site in which to escape the heat of the city.

Amateur interest in micrometeorology has risen sharply during the past decade as cooperative observers have learned its importance in analyzing local climate. Climatologists need to know at all times how much water is being held in the soil. It is very hard to get an accurate estimate of the evaporation from the soil or the transpiration of water by plants by any conventional means. Micrometeorology suggested a simple solution. Moisture escaping from the ground first enters a thin and relatively stationary "boundary layer" of air at the surface. It then diffuses into a relatively thick turbulent layer above, which carries it away. The mixing process tends to distribute moisture uniformly through the turbulent layer, but if water continues to enter the layer from the ground, the humidity is relatively high at the bottom of the layer and decreases with height above the surface. In other words, the layer shows a moisture gradient. Accordingly, micrometeorological measurements of temperature, wind velocity and humidity at successive intervals through the turbulent layer indicate the rate at which water is being carried away.

Frederick Lichtgarn, an amateur in Chicago, recently invented an electronic hydrograph element which he hopes will lead to the design of a direct-reading evaporation meter by utilizing the micrometeorological method. Lichtgarn's element, a specially processed ceramic, produces a voltage proportional to the vapor content of the air. When this voltage is combined through an appropriate analogue circuit with others proportional to temperature and wind velocity, the resulting voltage should represent the total transportation of moisture from the soil.

According to David Ludlum, a cooperative observer who combines pleasure with business by editing Weatherwise, the popular journal of the American Meteorological Society, you can't name a branch of science that is not intimately bound to meteorology in some way. That is why many meteorological amateurs parallel their enthusiasm for weather watching with an equal interest in some other field.

"I can name scores of cooperative observers," said Ludlum, "who go in for the earth sciences. When the study of today's climate fails to absorb enough free time, many of the fellows get fun out of checking up on the weather in their community as it used to be-not merely a decade or so ago but thousands or millions of years ago. During the Silurian and Jurassic periods the earth drifted along for thousands of years with one balmy day merging into the next. That is how periods like the Pennsylvania could produce such giant ferns and other lush vegetation. The times enjoyed an ideal balance of moisture and temperature.

"When an amateur meteorologist goes fossil hunting, he is looking for some thing more than a curio for his mantelpiece. The story he learns to read in the rocks adds to his knowledge of paleoclimatology. Not all amateurs live near a region that abounds in fossils, of course, but this does not bar the study of ancient climate to them. One advantage of climate as a hobby is the fact that we have weather everywhere-and always have had. So the fellow in Wisconsin or Iowa can go in for geochronologic climatology or documental climatology.

"Did you, as a boy, ever dig your bare toes into the mud of a pond or lake bottom when the water was low and wonder what caused the soil to settle in thin, sharp layers somewhat like tree rings? These layers are called 'varves.' During the rainy season run-off transports silt into the lake, where the coarse material drops to the bottom quickly. Then in winter when the surface freezes a second coat is added-a thin layer of material so fine that it takes many weeks to settle out of suspension. The combination of these two layers marks the passing of a year. Wet years produce thick varves and dry years thin ones-just as in the case of tree rings. The idea of using varves to extend investigations of climate back year by year was suggested by Gerard De Geer in 1878. An event which took place in Sweden some 150 years ago has enabled us to tie our own climatic chronology into varve geochronology. In 1796 the Swedes totally drained Lake Ragunda. Fortunately the operation did not destroy the uppermost varve; hence it is dated definitely. More than 1,100 others below it have been carefully counted and their thicknesses charted. Because no two years are identical climatically, each span of time is marked by its own 11 pattern of varves. Varves from one locality often can be matched up with those of another. That is how the record is extended, and persistent work has driven it back nearly 14,000 years.

"Only a few of the gang, so far as I know, go in for documental climatology to any extent. These amateurs browse through old manuscripts which, though usually written for some purpose unrelated to climate, give valuable clues -about it-the movement of populations, bumper crops, periods of famine, changes in trade routes forced by floods or droughts, mention of a rainless year. Several amateurs have used this method in extending the records of the U. S. climate back to the days of the first colonists. They comb old newspaper files and the archives of local historical societies for any bit they can find.

"Most of us, however, get all the paper work we want just keeping track of today's weather. We do not find that part of our hobby tedious or dull."

For several years ruling-engine experts (see SCIENTIFIC AMERICAN, June, July, August, 1953) have watched the progress of a new method of ruling diffraction gratings being developed in England by the spectroscopist Sir Thomas Merton and others. Merton has designed a machine which, instead of making parallel grooves by means of a diamond shuttling back and forth over a flat blank, rules a continuous spiral groove like a fine screw thread on a metal cylinder. The cylinder is then coated with a cellulose liquid which dries on as a thin film or skin. This cylindrical skin is slit lengthwise, peeled off like the bark of a tree, uncurled and mounted on flat glass for use.

Much research has been devoted to the improvement of this method by Merton, by R. G. N. Hall, G. D. Dew and L. A. Sayce of the British National Physical Laboratory and by the optical firm of Hilger and Watts, Ltd.

The Merton machine has met with the usual extremes of overenthusiastic praise and derision, according to the critics' predilections. Objective observers are waiting to see how it works out, remembering that in a century of ruling engine experimentation there have been many machines whose performance failed to equal the predictions that the experimenters were apparently unable to resist publishing.

The Merton principle is an attempt to get around the inherent difficulties of the traditional method-the uncertain positioning of the ruling diamond due to variations in lubrication as the engine continually stops and starts, and the residual errors in parts of the engine. It substitutes for the back-and-forth action "a continuous lathe-like action, avoiding all intermittent and reciprocating movements and maintaining constant stress in every component of the machine throughout the whole ruling operation." Yet the Merton method has its own inherent difficulties, which have only been partly remedied. Therefore the following is a progress report and not a final one.

The method in practice is not simple. No existing lathe can rule a spiral groove on a cylinder with enough precision to qualify as the matrix for duplicating a diffraction grating, in which the tolerance of error is only one millionth of an inch. It is uncertain that a perfect lathe can ever be built. Nevertheless Merton found a way to make a lathe accomplish the miracle of reproducing an almost perfect helix directly from an imperfect helix ruled by a lathe. Let's look at the apparatus that does this, shown in its original form by Roger Hayward's simplified drawing on page 116. A polished stainless steel cylinder an inch in diameter and a foot in length is put in precision lathe and threaded at 2,000 turns per inch for a distance of half its length plus an inch. This ruled helix will have all the serious periodic errors inherent in the lathe. Next a nut is run on the cylinder with an extension rod that places the diamond on the unruled portion. A wheel on the end of a side arm below the cylinder (see cut) keeps the nut from revolving while the cylinder rotates. (The means of rotation is not shown in the drawing.) The nut therefore moves along the cylinder. As it does so, the diamond rules a practically perfect secondary helix on the unruled part.

How can you rule a perfect helix from an imperfect one as a guide? Here is the answer. The threads of the nut consist of three small equally spaced strips of unthreaded cork coated with graphite, each about three eighths of an inch wide. The trick lies in the elasticity of the threads. The cork is elastic enough, or a part of it slips enough, or both, to average out the periodic errors of the primary grooves and produce almost perfect secondary grooves. The cylinders are practically free from taper and ellipticity and are honed and lapped optically smooth with pitch. This method of causing a part of a cylinder to act as its own lead screw also eliminates the thrust bearings that give trouble on conventional engines. Optical evidence in the Merton articles proves that the periodic errors due to the lathe practically disappear.

In 1950 Kenneth R. Eldridge, scientific liaison officer at the Office of the U. S. Naval Attaché in London, investigated the Merton machine and variations of it at the National Physical Laboratory and at Hilger and Watts. He found the Laboratory using a cylinder 1-1/2 by 12 inches, on which it had engraved a thread with a pitch of one 15,000th of an inch. The ruling was made with a simple lathe like an ordinary South Bend make. The thread of course was full of periodic errors. But in ruling the rest of the cylinder these errors were averaged out by the elastic follower nut already described. Since a diamond ground to simple knife-edge shape can be used as the ruling edge on the cylinder, the difficult technique of shaping a diamond for the oscillating type of ruling engine is simplified.

Eldridge found that Hilger and Watts had a machine which avoided the problem of optically finishing a long metal cylinder. The principle of their machine is shown in the upper left-hand drawing on page 117. It uses two short cylinders, each rotating in corklined end bearings having threads with zero pitch (closed rings instead of a helix). The lathe first engraves a coarse thread on the rear cylinder for a length of two inches. The thread has one thirtieth as many turns per inch as the final spacing desired for the grating; for example, it is ruled with 500 turns per inch to produce a grating with 15,000 turns per inch. A cork elastic nut is then mounted on the rear cylinder, and the front cylinder is rotated by outside means not shown. Because of the 1-to-30 gear ratio, the diamond, moved along the front cylinder by the nut on the rear cylinder, engraves on the front cylinder 30 grooves in the space of each groove on the rear cylinder.

A length of one inch is engraved by this method, and this will contain the errors of the gearing. These errors are then got rid of by mounting an elastic nut on the front cylinder, attaching the diamond to that nut and engraving a groove along its length (see drawing lower left). As the nut leaves the original one-inch of thread, it is picked up by the thread being engraved and carried forward, self-driven by the thread.

The physicist observer at the U. S. Office of Naval Research in London reported that in the experiments the progressive errors had proved to be very small, but that they remained a problem. Another problem was the fact that the delicate grooves already engraved were damaged when the elastic nut passed over them.

Last year Hall and Sayce of the National Physical Laboratory described some of the inherent faults of the Merton method. The helical grating still had two kinds of errors: periodic, caused by regularly repeated errors of pitch of the fine helix, and progressive, caused by comparatively slow and usually irregular variations of pitch. The principal problems in producing helical gratings are the elimination of these errors and the production of grooves of such profile that they will reflect and diffract the light in the same direction (blazed gratings). Two methods are being investigated.

The first method uses the gearing already described in a modified form (see drawing, left). A four-inch length of primary helix is cut on the rear cylinder with a single diamond. This helix therefore possesses all the progressive errors of four inches of the lathe's lead screw. A gang of four diamonds, or perhaps six, simultaneously cuts a four-inch length of helix on the front cylinder. By this dodge the helix ruled contains the progressive errors of only one inch of the lead screw, since only one inch of that screw has been used. The four portions of the composite helix may be out of phase with one another, but experiment shows that this does not adversely affect its guidance of the Merton nut on the rear cylinder. The subdivision of the primary helix may be further extended and the four diamonds multiplied indefinitely by substituting for the diamonds a six-inch strip of abrasive material (lower right-hand drawing). A few turns of the lathe inscribe on the front cylinder a large number of scratches, each with the correct helix angle. From this a Merton nut is found to inscribe a secondary helix free from both periodic and progressive errors. The method is not without practical difficulty, and its details have not yet been fully developed.

The second method being investigated attempts to escape from two difficulties: the damage to the primary helix when it is used for generating a secondary helix, and the fact that the grooves guide best when symmetrical in profile, while a symmetrical profile is rarely required in a grating. The solution, not shown in the drawings, is the use on the same cylinder of two trailing diamonds instead of one. The first rules the guiding grooves while the second is ruling a blazed grating groove some inches farther along.

Experimenters have found the pith of the elder tree, used by jewelers, to be an even better material than cork for the elastic nuts. If well lubricated, it shows no tendency to cause progressive error. Hidurex, an aluminum bronze, is a better material for the cylinders than steel. Cylinders an inch in diameter have proved most convenient.

Some critics, reasoning that these fantastic methods ought not to work, have therefore concluded that they do not work. They are partly correct. The proof of the pudding is not in the reasoning but in the gratings, which are good but not good enough. The spectra they make are said to be completely free from ghosts, but progressive errors remain.

In sum, the experimenters say they have been able to rule plane gratings 2-3/4 by 7 inches free from all periodic errors, with predetermined blaze. Most of these have been relatively coarse gratings, spaced 5,000 to 12,000 grooves in an inch. To try to rule finer gratings with the required freedom from progressive errors, the experimenters are building an improved lathe. They are also building an experimental engine to rule concave gratings. All this is the mechanical part of the Merton method. The final stage, most difficult of all, is to be able to reproduce the gratings ruled. Dew and Sayce reported in 1951 that they had developed a process by means of which they were able to achieve fidelity between the grating and replica, as far as spacing goes, within a very small fraction of a wavelength of light. Unfortunately the same replica may not be faithful in the shape and depth of the grooves. This essential problem, in addition to those already described, has therefore not yet been solved.

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