The Introduction of Self-Registering Meteorological Instruments Part 1

The Introduction of Self-Registering Meteorological Instruments.

by Robert P. Multhauf.

_The development of self-registering meteorological instruments began very shortly after that of scientific meteorological observation itself. Yet it was not until the 1860's, two centuries after the beginning of scientific observation, that the self-registering instrument became a factor in meteorology._

_This time delay is attributable less to deficiencies in the techniques of instrument-making than to deficiencies in the organisation of meteorology itself. The critical factor was the establishment in the 1860's of well-financed and competently directed meteorological observatories, most of which were created as adjuncts to astronomical observatories._

THE AUTHOR: _Robert P. Multhauf is head curator of the department of science and technology in the United States National Museum, Smithsonian Inst.i.tution._

The flowering of science in the 17th century was accompanied by an efflorescence of instrument invention as luxurious as that of science itself. Although there were foreshadowing events, this flowering seems to have owed much to Galileo, whose interest in the measurement of natural phenomena is well known, and who is himself credited with the invention of the thermometer and the hydrostatic balance, both of which he devised in connection with experimentation on specific scientific problems. Many, if not most, of the other Italian instrument inventors of the early 17th century were his disciples. Benedetto Castelli, being interested in the effect of rainfall on the level of a lake, constructed a rain gauge about 1628. Santorio, well known as a pioneer in the quantification of animal physiology, is credited with observations, about 1626, that led to the development of the hygrometer.

Both of these contemporaries were interested in Galileo's most famous invention, the thermoscope--forerunner of the thermometer--which he developed about 1597 as a method of obtaining comparisons of temperature. The utility of the instrument was immediately recognized by physicists (not by chemists, oddly enough), and much ingenuity was expended on its perfection over a 50-year period, in northern Europe as well as in Italy. The conversion of this open, air-expansion thermoscope into the modern thermometer was accomplished by the Florentine Accademia del Cimento about 1660.

Galileo also inspired the barometer, through his speculations on the vacuum, which, in 1643, led his disciple Torricelli to experiments proving the limitation to nature's horror of a vacuum. Torricelli's apparatus, unlike Galileo's thermoscope, represented the barometer in essentially its cla.s.sical form. In his earliest experiments, Torricelli observed that the air tended to become "thicker and thinner"; as a consequence, we find the barometer in use (with the thermometer) for meteorological observation as early as 1649.[1]

The meetings of the Accademia terminated in 1667, but the 5-year-old Royal Society of London had already become as fruitful a source of new instruments, largely through the abilities of its demonstrator, Robert Hooke, whose task it was to entertain and instruct the members with experiments. In the course of devising these experiments Hooke became perhaps the most prolific instrument inventor of all time. He seems to have invented the first wind pressure gauge, as an aid to seamen, and he improved the bathometer, hygrometer, hydrometer, and barometer, as well as instruments not directly involved in measurement such as the vacuum pump and sea-water sampling devices. As in Florence, these instruments were immediately brought to bear on the observation of nature.

It does not appear, however, that we would be justified in concluding that the rise of scientific meteorology was inspired by the invention of instruments, for meteorology had begun to free itself of the traditional weather-lore and demonology early in the 17th century. The Landgraf of Hesse described some simultaneous weather observations, made without instruments, in 1637. Francis Bacon's "Natural History of the Wind,"

considered the first special work of this kind to attain general circulation, appeared in 1622.[2] It seems likely that the rise of scientific meteorology was an aspect of the general rationalization of nature study which occurred at this time, and that the initial impetus for such progress was gained not from the invention of instruments but from the need of navigators for wind data at a time when long voyages out of sight of land were becoming commonplace.

[Ill.u.s.tration: Figure 1.--A set of typical Smithsonian meteorological instruments as recommended in instructions to observers issued by the Inst.i.tution in the 1850's. _Top_ (from left): maximum-minimum thermometer of Professor Phillips, dry-bulb and wet-bulb thermometers, and mercurial barometer by Green of New York. _Lower left:_ rain gauge.

The wet-bulb thermometer, although typical, is actually a later instrument. The rain gauge is a replica. (_Smithsonian photo 46740._)]

It should be noted in this connection that the two most important instruments, the thermometer and barometer, were in no way inspired by an interest in meteorology. But the observation made early in the history of the barometer that the atmospheric pressure varied in some relationship to visible changes in the weather soon brought that instrument into use as a "weather gla.s.s." In particular, winds were attributed to disturbances of barometric equilibrium, and wind-barometric studies were made by Evangelista Torricelli, Edme Mariotte, and Edmund Halley, the latter publishing the first meteorological chart. In 1678-1679 Gottfried Leibniz endeavored to encourage observations to test the capacity of the barometer for foretelling the weather.[3]

Other questions of a quasi-meteorological nature interested the scientists of this period, and brought other instruments into use.

Observations of rainfall and evaporation were made in pursuit of the ancient question of the sources of terrestrial water, the maintenance of the levels of seas, etc. Physicians brought instruments to bear on the question of the relationship between weather and the incidence of disease. The interrelationship between these various meteorological enterprises was not long in becoming apparent. Soon after its founding in 1657 the Florentine academy undertook, through the distribution of thermometers, barometers, hygrometers, and rain gauges, the establishment of an international network of meteorological observation stations, a network which did not survive the demise of the Accademia itself ten years later.

Not for over a century was the first thoroughgoing attempt made at systematic observation. There was a meteorological section in the Academy of Sciences at Mannheim from 1763, and subsequently a separate society for meteorology. In 1783, the Academy published observations from 39 stations, those from the central station comprising data from the hygrometer, wind vane (but not anemometer), rain gauge, evaporimeter, and apparatus for geomagnetism and atmospheric electricity, as well as data from the thermometer and barometer. The Mannheim system was also short-lived, being terminated by the Napoleonic invasion, but systems of comparable scope were attempted throughout Europe and America during the next generation.

In the United States the office of the Surgeon General, U. S. Army, began the first systematic observation in 1819, using only the thermometer and wind vane, to which were added the barometer and hygrometer in 1840-1841 and the wind force anemometer, rain gauge, and wet bulb thermometer in 1843. State weather observation systems meanwhile had been inaugurated in New York (1825), Pennsylvania (1836), and Ohio (1842).[4]

Nearly 200 years of observation had not, however, noticeably improved the weather, and the naive faith in the power of instruments to reveal its mysteries, which had possessed many an early meteorologist, no longer charmed the scientist of the early 19th century. In the first published report of the British a.s.sociation for the Advancement of Science in 1833, J. D. Forbes called for a reorganization of procedures:

In the science of Astronomy, for example, as in that of Optics, the great general truths which emerge in the progress of discovery, though depending for their establishment upon a mult.i.tude of independent facts and observations, possess sufficient unity to connect in the mind the bearing of the whole; and the more perfectly understood connexion of parts invites to further generalization.

Very different is the position of an infant science like Meteorology. The unity of the whole ... is not always kept in view, even as far as our present very limited general conceptions will admit of: and as few persons have devoted their whole attention to this science alone ... no wonder that we find strewed over its irregular and far-spread surface, patches of cultivation upon spots chosen without discrimination and treated on no common principle, which defy the improver to inclose, and the surveyor to estimate and connect them. Meteorological instruments have been for the most part treated like toys, and much time and labor have been lost in making and recording observations utterly useless for any scientific purpose. Even the numerous registers of a rather superior cla.s.s ... hardly contain one jot of information ready for incorporation in a Report on the progress of Meteorology....

The most general mistake probably consists in the idea that Meteorology, as a science, has no other object but an experimental acquaintance with the condition of those variable elements which from day to day const.i.tute the general and vague result of the state of the _weather_ at any given spot; not considering that ...

when grouped together with others of the same character, [they] may afford the most valuable aid to scientific generalization.[5]

Forbes goes on to call for a greater emphasis on theory, and the replacement of the many small-scale observatories with "a few great Registers" to be adequately maintained by "great Societies" or by the government. He suggests that the time for pursuit of theory might be gained from "the vague mechanical task to which at present they generally devote their time, namely the search for great numerical accuracy, to a superfluity of decimal places exceeding the compa.s.s of the instrument to verify."

From its founding the British a.s.sociation sponsored systematic observation at various places. In 1842 it initiated observations at the Kew Observatory, which has continued until today to be the premier meteorological observatory in the British Empire. The American scientist Joseph Henry observed the functioning of an observatory maintained by the British a.s.sociation at Plymouth in 1837, and when he became Secretary of the new Smithsonian Inst.i.tution a few years later he made the furtherance of meteorology one of its first objectives.

The Kew Observatory set a pattern for systematic observation in England as, from 1855, did the Smithsonian Inst.i.tution in the United States. The instruments used differed little from those in use at Mannheim over half a century earlier[6] (fig. 1). They were undoubtedly more accurate, but this should not be overstressed. Forbes had noted in his report of 1832 that some scientists were then calling for a return to Torricelli, for the construction of a temporary barometer on the site in preference to reliance on the then existing manufactured instruments.

The First Self-Registering Instruments

From the middle of the 17th century meteorological observations were recorded in ma.n.u.script books known as "registers," many of which were published in the early scientific journals. The most effective utilization of these observations was in the compilation of the history of particular storms, but where a larger synthesis was concerned they tended, as Forbes has shown, to show themselves unsystematic and non-comparable. The princ.i.p.al problems of meteorological observation have been from the outset the construction of precisely comparable instruments and their use to produce comparable records. The former problem has been frequently discussed, and perhaps, as Forbes suggests, overemphasized. It is the latter problem with which we are here concerned.

The idea of mechanizing the process of observation, not yet accomplished in Forbes' time, had been put forward within a little over a decade of the first use of the thermometer and barometer in meteorology. On December 9, 1663, Christopher Wren presented the Royal Society with a design for a "weather clock," of which a drawing is extant.[7] This drawing (fig. 2) shows an ordinary clock to which is attached a pencil-carrying rack, geared to the hour pinion. A discussion of the clock's "reduction to practice" began the involvement of Robert Hooke, who was "instructed" in September 1664 to make "a pendulum clock applicable to the observing of the changes in the weather."[8] This tribute to Hooke's reputation--and to the versatility of the mechanic arts at this time--was slightly overoptimistic, as 15 years ensued before the clock made its appearance.

[Ill.u.s.tration: Figure 2.--A contemporary drawing of Wren's "weather clock." (Photo courtesy Royal Society of London.)]

References to this clock are frequent in the records of the Royal Society--being mainly periodic injunctions to Hooke to get on with the work--until its completion in May 1679. The description which Hooke was asked to supply was subsequently found among his papers and printed by William Derham as follows:[9]

The weather-clock consists of two parts; _first_, that which measures the time, which is a strong and large pendulum-clock, which moves a week, with once winding up, and is sufficient to turn a cylinder (upon which the paper is rolled) twice round in a day, and also to lift a hammer for striking the punches, once every quarter of an hour.

_Secondly_, of several instruments for measuring the degrees of alteration, in the several things, to be observed. The first is, the barometer, which moves the first punch, an inch and half, serving to shew the difference between the greatest and the least pressure of the air. The second is, the thermometer, which moves the punch that shews the differences between the greatest heat in summer, and the least in winter. The third is, the hygroscope, moving the punch, which shews the difference between the moistest and driest airs. The fourth is, the rain-bucket, serving to shew the quant.i.ty of rain that falls; this hath two parts or punches; the first, to shew what part of the bucket is fill'd, when there falls not enough to make it empty itself; the second, to shew how many full buckets have been emptied. The fifth is the wind vane; this hath also two parts; the first to shew the strength of the wind, which is observed by the number of revolutions in the vane-mill, and marked by three punches; the first marks every 10,000 revolutions, the second every 1,000, and the third every 100: The second, to shew the quarters of the wind, this hath four punches; the first with one point, marking the North quarters, viz.

N.: N. by E.: N. by W.: NNE.: NNW.: NE. by N. and N.W. by N.: NE.

and N.W. The second hath two points, marking the East and its quarters. The third hath three points, marking the South and its quarters. The fourth hath four points, marking the West and its quarters. Some of these punches give one mark, every 100 revolutions of the vane-mill.

The stations or places of the first four punches are marked on a scrowl of paper, by the clock-hammer, falling every quarter of an hour. The punches, belonging to the fifth, are marked on the said scrowl, by the revolutions of the vane, which are accounted by a small numerator, standing at the top of the clock-case, which is moved by the vane-mill.

What, exactly, were the instruments applied by Hooke to his weather clock? It is not always easy even to guess, because it appears that Wren was actually the first to contrive such a device and seems to have developed nearly as many instruments as Hooke. It might be supposed that Hooke would have adapted to the weather clock his wheel-barometer, introduced in 1667, but it also appears that Wren had described (and perhaps built) a balance barometer before 1667.[10] As to the thermometer, we have no evidence of original work by Hooke, but we do have a description of Wren's self-registering thermometer, a circular, mercury-filled tube in which changes in temperature move "the whole instrument, like a wheel on its axis."[11]

The hygroscope (hygrometer) probably existed in more versions than any other instrument, although we know nothing of any versions by Wren.

Hooke may have used his own "oat-beard" instrument.[12] Derham follows his description of the clock--which has been quoted above--with a detailed description of a tipping-bucket rain gauge invented by Hooke and used with the clock. He also notes that in 1670 Hooke had described two other types of rain gauge in which a bucket was counterbalanced in one case by a string of bullets and in another by an immersed weight.

But here again, Sprat records the invention of a tipping-bucket gauge by Wren before 1667.

Hooke has been generally regarded as the first inventor of an anemometer, in 1662.[13] But this invention was a pressure-plate gauge--that is, a metal plate held with its face against the wind--whereas the gauge used with the weather clock is clearly a windmill type, of which type this may be the first. Wren also had an anemometer, but we have no description of it. Hooke's account does not refer to other instruments which the weather clock is supposed to have had, according to a description quoted by Gunther, which concludes the enumeration of the elements recorded with "sunshine, etc."[14] One can only wish for further information on the mechanism by which the punches--or in Wren's clock, the pencils--were moved. But it is apparent that Hooke's clock was actually used for some time.

[Ill.u.s.tration: Figure 3.--Dolland's "atmospheric recorder": 1, siphon and float barometer; 2, balance (?) thermometer; 3, hygrometer; 4, electrometer; 5, float rain gauge; 6, float evaporimeter; 7, suspended-weight wind force indicator; 8, wind direction indicator; 9, clock; 10, receivers for rain gauge and evaporimeter. (From _Official ... Catalogue of the Great Exhibition, 1851,_ London, 1851, pt. 2).]

The 17th century was not entirely unprepared for the idea of such a self-registering instrument. Water clocks and other devices in which natural forces governed a pointer were known in antiquity, as were counters of the type of the odometer. A water clock described in Italy in 1524 was essentially an inversion of one of Hooke's rain gauges, that in which a bucket was balanced against a string of bullets.[15] The mechanical clock also had a considerable history in the 17th century, and had long since been applied to the operations of figures through cams, as was almost certainly the case with the punches in Hooke's clock. Still, the combination of an instrument-actuated pointer with a clock-actuated time-scale and a means of obtaining a permanent record represent a group of innovations which certainly ranks among the greatest in the history of instrumentation. It appears that we owe these innovations to Wren and Hooke.

Hooke's clock contributed nothing to the systematization of meteorological observation, and the last record of it appears to have been a note on its "re-fitting" in 1690. Its complexity is sufficient reason for its ephemeral history, but complexity in machine design was the fashion of the time and Hooke may have intended no more than a mechanistic _tour de force_. On the other hand, he may have recognized the desideratum to which later meteorologists frequently returned--the need for simultaneous observations of several instruments on the same register. In any case, no instrument so comprehensive seems to have been attempted again until the middle of the 19th century, when George Dolland exhibited one at the Great Exhibition in London (see fig. 3).

The weather elements recorded by Dolland's instrument were the same as those recorded by Hooke's, except that atmospheric electricity (unknown in Hooke's time) was recorded and sunshine was not recorded. Striking hammers were used by Dolland for some of the instruments and "ever pointed pencils" for the others. Dolland's barometer was a wheel instrument controlling a hammer. His thermometric element consisted of 12 balanced mercury thermometers. Its mode of operation is not clear, but it probably was similar to that of the thermometer developed by Karl Kreil in Prague about the same time (fig. 4). Dolland's wind force indicator consisted of a pressure plate counterbalanced by a string of suspended weights. Altogether, it is not clear that Dolland's instrument was superior to Hooke's, or that its career was longer.[16]

The 171 years between these two instruments were not lacking in inventiveness in this field, but even though inventors set the more modest aim of a self-recording instrument for a single piece of meteorological data, their brain children were uniformly still-born.

Then, during the period 1840-1850, we see the appearance of a series of self-registering instruments which were actually used, which were widely adopted by observatories, and which were superseded by superior instruments rather than abandoned. This development was undoubtedly a consequence of the establishment at that time of permanent observatories under competent scientific direction.

Long experience had demonstrated to the meteorologists of the 1840's that the princ.i.p.al obstacle to the success of self-registering instruments was friction. Forbes had indicated that the most urgent need was for automatic registration of wind data, as the erratic fluctuation of the wind demanded more frequent observation than any manual system could accomplish. Two of the British a.s.sociation's observers produced separate recording instruments for wind direction and force in the late 1830's, a prompt response which suggests that it was not the idea which was lacking. One of these instruments--designed by William Whewell--contained gearing, the friction of which vitiated its utility as it had that of a number of predecessors. The other, designed by A.

Follet Osler, was free of gearing; it separately recorded wind pressure and direction on a sheet of paper moved laterally by clockwork. The pressure element was a spring-loaded pressure plate carried around by the vane to face the wind. Both this plate and the vane itself were made to move pencils through linkages of chains and pulleys.[17] Osler's anemometer (fig. 5) deserves to be called the first successful self-registering meteorological instrument; it was standard equipment in British observatories until the latter part of the 19th century when it was replaced by the cup-anemometer of Robinson.

[Ill.u.s.tration: Figure 4.--Kreil's balance thermometer, 1843. (From Karl Kreil, _Magnetische und meteorologische Beobachtungen zu Prag_, Prague, 1843, vol. 3, fig. 1.)]

[Ill.u.s.tration: Figure 5.--Osler's self-registering pressure plate anemometer, 1837. The instrument is shown with a tipping-bucket rain gauge. (From Abbe, _op. cit._ footnote 17.)]

Self-recording barometers and thermometers were more vulnerable to the influence of friction than were wind instruments, but fortunately pressure and temperature were also less subject to sudden fluctuation, and so self-registration was less necessary. Nevertheless, two events occurred in the 1840's which led to the development of self-registering instruments. One event was the development of the geomagnetic observatory, which used the magnetometer, an instrument as delicate as the barometer and thermometer, and (as it then seemed), as subject to fluctuation as the wind vane. The other event was the development of photography, making possible a recording method free of friction. In 1845 Francis Ronalds at Kew Observatory and Charles Brooke at Greenwich undertook to develop apparatus to register the magnetometer, electrometer, thermometer, and barometer by photography.[18] This was six years after Daguerre's discovery of the photographic process. The magnetometers of both investigators were put into use in 1847, and the barometers and thermometers shortly after. They were based on the deflection--by a mirror in the case of the magnetometer and electrometer and by the mercury in the barometer and thermometer--of a beam of light directed against a photographic plate. Brooke exhibited his instruments at the Great Exhibition of 1850, and they subsequently became items of commerce and standard appurtenances of the major observatory until nearly the end of the century (fig. 6). Their advantages in accuracy were finally insufficient to offset the inconvenience to which a photographic instrument was subject.

Before 1850 the British observatories at Kew and Greenwich (the latter an astronomical observatory with auxiliary meteorological activity) had self-registering apparatus in use for most of the elements observed.