Paolo Brenni on Lightning Recorders
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Written by Lightning A short story of lightning recorders: ceraunographs, electrographs, klydonographs Part 1 From Becaria’s Ceraunograph to Gergely Palatin’s Detector Paolo Brenni Foreword a lightning discharge was strong or close Since the mid-18th century atmospheric elec- enough to the ceraunograph a spark jumped tricity both in fair weather and during thun- between the gap of the conductors and perfo- derstorms was detected and measured with rated the paper disk. From the size of the hole a series of instruments such as spark gaps, it was possible to estimate the intensity of the electric chimes, electroscopes, electrometers lightning. From its position on the disk with and later galvanometers, which were gener- respect to the XII hour line, it was possible to ally connected with an aerial.1 Lightning re- determine the time of the discharge. Further- cording devices were mainly developed in the more, according to Beccaria, if the position of framework of wireless technology, between the hole corresponded to the upper electrode the very end of the 19th n frst yers of the (1), the lightning occurred downward from the 20th century, but their origins go back to the clouds to the earth. On the other hand, a hole ceraunographs proposed in the 1780s. In this aligned with the lower grounded electrode (2) article in two parts I will retrace the history of indicated an upward discharge from the earth 5 the instruments which allowed to register di- to the clouds. However, the ceraunograph rectly (on er resin hotorhic flm etc.) was a very imperfect instrument. The sparks lightning strikes or sudden variations of atmo- produced by two or more lightning events in sheric electricity fel urin thunerstorm. rapid succession proceeded to pass throughout a single hole instead of perforating the paper Beccaria’s Ceraunograph and its several times.6 Furthermore, sometimes the Modifcations spark did not perforate the disk in correspon- Giovanni Battista Beccaria (1716–1781), the dence with one of the electrodes, but some- renowned Italian “electrician” taught phys- where between them. ics in rious Itlin cities n fnlly occu- Beccri s not stisfe ith this frst pied the chair of experimental physics at the apparatus and in the same paper he proposed University of Turin. He was an excellent ex- a second improved version. There is no origi- erimenter n his reserches in the fel of nal illustration of it, but from the description electricity (in which he supported Franklin’s Fig. 1 The original ceraunograph described I could draw an ideal reconstruction. (Fig. sinle ui theory) ere mon the most re- by Beccaria. The top image shows the disk 2) The instruments consisted of four parallel markable of his time. In 1780, Beccaria de- inserted on the clockwork mechanism. P and and horizontal cylinders, which could rotate scrie the frst lihtnin recorin rtus S are the electrodes connected respectively easily. Two of them were placed higher than 2 and also invented its name – ceraunograph. with the lightning rod and with the ground. the other. A paper roll was wrapped on the The term derives from the Greek words In the other images the instrument in its box frst cyliner. he er te sse eteen 3 (thunerolt) n (to rite). with the horary dial. (Beccaria 1780, op. cit. the two electrodes (1 and 2) over the pair of note 2). Beccris frst cerunorh s comose higher cylinders and was rewound of a clockwork mechanism with a vertical axle on the last one. This was connected (Fig. 1). A horizontal recording paper disk was with a rope to the driving weight of inserted on it. The disk was supported by a a pendulum clock. The descent of series of radial straws inserted in the axle. A the weight moved the cylinder and t circulr o ith circulr oenin ro- rewound the tape. Finally, a counter- tected the clockwork. The rim of the opening eiht on the frst cyliner et the carried a horary annular-shaped scale divided tape in tension. With a long tape, on in 12 hours and minutes. A radial line had to which there was a horary scale for be marked on the recording disk in correspon- many days, it was possible to have a dence of the XII (midday or midnight), so long recording with several thunder- that it was possible to have a time reference. storms registered. By using a clock The pointed lower end of an aerial conductor4 with a long and relatively fast move- (electrode 1) terminated near the upper face of ment of the descending weight, the the paper disk, while the upper end of a second risk of having a single hole for more wire (electrode 2), which was grounded, end- than one spark was reduced. ed near the lower face of the disk. The termi- Unfortunately due to his poor health, nals of the two electrodes were aligned along Beccaria could not experiment with a same radius of the disk, but their distances Fig. 2 A modern illustration reconstructing the second version of Beccaria’s ceraunograph. from the centre were slightly different. The electric discharges were recorded on a long roll of paper passing between the two During a thunderstorm, lightning induced electrodes. The inscribed paper was rolled around a cylinder moved by the falling weight of a voltage surges in the aerial conductor. If pendulum clock. (Diagram of the author). 2 Bulletin of the Scientifc Instrument Society No. 145 (2020) Fig. 4 The very complicated meteorograph proposed by Vassalli-Eandi. The recording anemometer and a recording wind vane with their recording drum are on the left; the barograph and the thermograph together with a clock are placed in the centre, while on the right there is the ceraunograph. The latter was actioned by a glass rod connected with the clockwork of the Fig. 3 Cavalli’s cronio-ceraunometer. The croniometer recorded anemograph. (Vassalli-Eandi. 1803-4, op. cit. note 12). the hour and then quantity of rain on the internal ring of the clockwork driven disk. The quadrangular funnel collected the rain which flled the small vessel fxed on the lever with a pen. and marked a trace on Electric discharges were recorded with the ceraunograph on it.10 When the rain ceased the external part of the disk. The bar connected to the lightning the vessel was completely rod and the one going to the ground are equipped with quadrant emptied by a special sy- electrometers. (Cavalli, 1785, op. cit. note 8). phon and the action of the spring raised the lever. this second ceraunograph. But an almost iden- With Landriani’s apparatus it was possible to tical instrument was made following Becca- record the hours of rain and because the wa- ria’s suggestion by Francesco Giuseppe Gar- ter coming from the vessel was collected in a dini (1740–1816) a physician and natural phi- graduated cylinder so that it was also possible losopher, who had been a disciple of Beccaria to measure the quantity of fallen rain. Cavalli himself.7 Gardini described his ceraunograph rofte from the fct tht oth the chroniom- in 1785 and extensively used it in his studies eter and the ceraunograph were equipped with on the inuence of electricity on lnts. a rotating recording disk. With the chronio-ce- In the same year, the Roman abbot and astron- raunograph it was possible to record one near omer Atanasio Cavalli (1729–1797) described the other and on the same disk the hours of rain a new instrument which he baptised with the as well as the time of the electric discharges. name of cronio-ceraunometer8 (Fig. 3). This By comparing the two traces one could at- s the comintion of the frst Beccris ce- tempt to establish some relationship between Fig. 5 The detail of the ceraunograph raunograph with a recording rain gauge, which the two meteorological phenomena. The in- illustrated in the previous image. The had been invented by the Italian chemist, strument was installed in the Roman private electrode connected with the lightning physicist and meteorologist Marsilio Landri- observatory known as Specola Caetani.11 rod ended near the upper face of the disk. ani (1751–1815). In Landriani’s Chroniho- It was also connected with a gold leaves Around 1800 the Italian physicist and math- metro9 the rain was collected by a funnel and electroscope, which detected the atmospheric ematician Antonio Vassalli Eandi (1761– throuh ie tht flle smll essel lce electricity when this was too weak for 1825) proposed a complex meteorograph.12 at one of the extremities of a lever connected producing a spark across the disk. (Vassalli- The apparatus included an anemograph and to a spring. A pencil was inserted vertically in Eandi. 1803-4, op. cit. note 12). a wind vane, a barograph, a thermograph the same lever and under it there was a rotat- and a Beccaria’s ceraunograph13 (Fig. 4). ing disk with a horary scale mounted on the The disk of the ceraunograph rotated thanks transmitted to the disk via a connecting glass axle of a clockwork mechanism. During the to the clockwork moving the recording drum shaft and some gears (Fig. 5). But this mete- hours of rain the weight of the vessel (which of the anemograph. The ceraunograph was orograph was probably never constructed. In remained full of water) lowered the lever and located in a separate electric pavilion and the 1780s the Italian physician Pietro Moscati thus the pencil was in contact with the disk therefore the movement of the clockwork was (1124) ho s intereste in the inu- Bulletin of the Scientifc Instrument Society No.