February 23, 189^ 



NATURE 



)93 



was observed. A figure is given of an observation at 

 Terre Haute, Ind., on a day when a fog formed after sun- 

 set, and the potential then rapidly fell from + looo to 

 -200 volts." "The same phenomenon was frequently 

 observed during the autumn when the formation of a haze 

 or fog just as the sun was setting was a common 

 occurrence." 



The observer at Terre Haute (Sergeant McRae) wisely 

 made special observations as to the possible effect of 

 locomotives on a railway a quarter of a mile distant ; 

 but, so far as the recods show, the passage of a train, 

 when not happening to coincide with a fog formation, 

 did not seem to disturb the curves. 



Clouds and Wind. 



" The direct action of a cloud or group of clouds in 

 producirii^ a fall of potential was often observed." 

 For instance the following at Boston : — "In the 

 morning of January 3, 1888, the potential had been 

 steadily' positive. At 11.30 it was -f 32 volts, from which 

 it fell steadily at the approach toward the zenith of a 

 small cumulus cloud, reaching - 21 volts As the cloud 

 passed away the potential rose to + 6, again falling to 

 - 31 as a large mass of cumulus clouds approached. 

 Later the sky became overcast, and the potential became 

 steadily negative. 



" On June 7, at 5.30 p.m., the potential fell from + 43 

 to - 173, and then rose slowly to its former value. The 

 rise and fall occupied fifteen minutes, and coincided with 

 the appearance over the buildings to the west of a fleecy 

 cirro-stratus cloud and its disappearance over the institute 

 building in which the electrometer was located. 



" Again, on June 9 the potential was positive all day up 

 to 5 p.m. At that hour it fell from -j- 73 to - 113, then 

 rising to + 52. The sky was nearly free from clouds, and 

 the fluctuation coincided with the approach and departure 

 of a cirro-stratus cloud, passing about 15^ from the 

 zenith. The inductive action of the cloud was plainly 

 suggested in all of these cases." 



High wind also usually causes a drop of potential. 



Averages. 



Some charts are then given of average monthly 

 potentials, showing nearly always positive average values, 

 highest in the winter, lowest in summer. 



Some smoothed diurnal curves are also given, and 

 "seem to indicate the existence of two principal maxima 

 of potential in the day, and also in a general way that 

 one of these occurs not many hours before noon and the 

 other toward the latter part of the day." 



Thunderstorms. 

 Special attention was paid to the observations before, 

 during, and after the occurrence of thunderstorms, but 

 the needle then dashes wildly to either side, and sparks 

 often begin to pass. And the' remark is made : — " Aside 

 from the general characteristics (rapidity and range of 

 fluctuation) these potential curves seem to have little in 

 common. The examination of a few cases only might 

 lead to interesting conclusions, which would almost cer- 

 tainly be overthrown by the study of a greater number. 

 Sometimes the potential falls rather steadily until the 

 violent movements begin, but sometimes it rises just as 

 long and steadily. In many cases the fluctuations start 

 from a high positive, while in many others the reverse is 

 the case. The storm is usually accompanied by precipi- 

 tation ; sometimes this begins before the needle starts on 

 its series of swings from side to side, and sometimes these 

 movements precede precipitation. The steady rise of 

 potential for some hours immediately following a thunder- 

 storm may mean that clear and fair weather is to be ex- 

 pected, but Fig. 71 is good evidence that it may also be 

 mterpreted to mean that another thunderstorm is just 

 at hand." 



NO. 12 17, VOL. 47] 



" Although these records are somewhat unsatisfactory 

 as far as throwing any light upon the nature of thunder- 

 storms, it must not be forgotten that with a single 

 exception [two stations at Washington] none of these 

 storms have influenced more than one station. The 

 complete investigation of a storm would demand a large 

 number of observing stations relatively near to each 

 other, by means of which a full history of the potential 

 changes about and in all parts of the storm could be 

 obtained. 



" Such an examination might result in bringing order 

 and system out of what seems at present little less than 

 confusion." 



Then follow many specimens of the actual photographic 

 record at Baltinibre on days when lightning occurred, 

 and finally a niass of tables embodying abstracts of 

 results at the different stations, and also some taken at 

 Kew and Gree'il'wkh in England ; though at both of 

 these insti^tutions the scale used appears to be arbitrary. 



General Conclusions. 



Among the conclusions the following may be noted : 

 " Instruments similar in every respect, separated by a 

 distance of a hundred meters may give very dissimilar 

 indications." (Not merely, it is explained, as regards 

 absolute values only, which may be expected to disagree, 

 but as regards fluctuations also.) " Observers were in- 

 structed to study the appearance of negative electricity 

 before and after and during precipitations, and at one 

 time the hope was indulged in by the writer, as well as 

 by several of the observers, that this phenomenon might 

 afford great assistance in the prediction of local storms, 

 rains, snows, &c., which offer so much difficulty in 

 forecasting by present methods. 



" Further observation and investigation, however, did 

 not justify this expectation, serving rather to increase 

 the meteorological conditions under which negative po- 

 tential might be looked fcr, and to diminish the defini- 

 tion of relationship between it and precipitation. That 

 negative electricity is tolerablv certain to be observed 

 in connection with precipitation in a majority of cases 

 is doubtless true, but it does not appear in such a way 

 as to be of any value in forecasting." 



Near the end of the historical introduction we learn 

 with regret that the observations thus tabulated and 

 discussed are now no longer going on. 



" In August, 1888, all observations were discontinued. 

 It was thought that a sufficient number had been accu- 

 mulated to decide the question of their use in weather 

 forecasting, and in fact their study up to that date gave 

 little encouragement in that direction." " Many ques- 

 tions of great scientific interest . . . had to be set aside 

 for those likely to be of immediate practical value." 



The amount of material thus rapidly accumulated, 

 centralised, and well discussed, is typical of what can be 

 done under efficient Government authorisation and by 

 the head of a National Laboratory. The carrying on of 

 the research for immediate utilitarian ends, and stopping 

 it as soon as it was seen that the results aimed at were 

 not forthcoming, is perhaps also typical. 



It is to be hoped that some day the question will be 

 reopened, and a fresh series of results obtained. So far 

 as I (who am by no means a meteorologist) can judge, I 

 should surmise that a number of fairly concentrated 

 stations over a large plain would be desirable ; and also 

 that the vertical gradient of potential should be attempted 

 by a series of collectors at different attitudes on a tall 

 mast, or possibly up a hill-side. 



Further, the general aspect of the curves seems to me 

 to suggest that the instruments were almost too sensitive 

 and not sufficiently dead-beat. They should be quick 

 in indication and at the same time thoroughly damped, 

 so that the record shall contain as little as possible of 

 any effect due to instrumental inertia. Some very light 



