162 MONTHLY WEB
A WIRELESS STORM DETECTOR FOR THE CENTRAL LIQHTINO STATION.
By HERBERT T. WADE.
(Abstracted Irom Scientific Ammican Monthly. January. 1920, vol. 1, pp. 18-21.)
At large power stations, such as that of the Waterside Station of the New York Edison Co.. considerable diffi- culty in su plying sufficient current, may arise wit.11 a sudden dar R ening of the sky at unusual times. This is
often true of thunderstorms, when the sky will become dark almost without warning, ancl thousands of lights will be switched on all over the city almost instantly, increasing the load t.0 such an estent that tlie power
meet the demand. The
the central station. To combat this the Waterside Station has had mount,ed on its roof for several years wireless anteniis so arranged that the. electrical impulses from a very distant, thun- derstorm are caused to rin a bell in an office below.
visible signs of its presence the bell will ring every few minutes, with increashia frequency as the storm approaches, until filially wyien the st,orm may st,ill be an
hour away, the bell will ring const,antly. This gives a warning of several hours, w1iic.h is quite sufficient t.0 call into service boilers which have been banked. Hence, when the storm breaks and the city calls sucldenly for li ht these reserve boilers will have steam ready to turn a % ditional dynamos and supply the required current.-
c. L. a.
station, unless prepared
tional rotary converters, but the
When the storm is 100 mi f es away, and there are no
(Abstracted
THE AUDIBILITY OF THUNDER.
By C. VEENEMA.
from Das R'cttrr June 1817 Dec., 1917,'pp. 2rls-hjzf 127-130; Aug.-SS t Er.-Apr., ~gis, ai. j'
1917, pp. 18i-192;
There are two met,liods of determining the distance of thunder sources-the first by measuring t e actual
interval between light,ning and thunder. The first method requires at least two obserrers, or as many more as possible, who will report the time of first tliunder, the time of nearest approach of the storm, and whet.lier or not the storm passed directly over the observer. 111 this. manner the path of t.he st,orm can be const,ruct.ed ver)-
accurately, and the distance of the t,hunder determined for any time from a given st.ation. This plan is not feasible for storms approaching from the sea or for t.liose observed over t,he sea. There is also danger thitt t.he first thuider may be confused with other noises, or that the direction may be in error, but these difficultie. s nre largely overcome with pract,ice. The second niet.lioc1, that of determining distance by time interval between lightning and thunder, has ndran tages and clisndvan- tages also. Only one observer is needed! ancl the results of his observation can be obtained at once. On t.he other hand, when there is continuous thunder and frequent li htning, especially at ni ht., when ot,lier
hility are propitious, it is often difficult. bo associate a
ven peal of thunder with its proper flash of lightning.
fi oreover, the circumstances surrounding the ohserver must be favorable, or, as frequentlV happened to the author, the observation will be lost hy the passing of a
wagon, the roar of the wind, or the noise of the rain, after having counted seconds for a considerable period.
distance and the second by det,eimiining P .lie time
conditions P or obtaining large values P or t,hunder audi-
,THER REVIE'W. MARCH, I920
By almost continuous observation of thunderstorms from 1F95 t,o 1916 the following distances occurred for a certain group of observations: On 9 occ.asions, between 30 and 40 kilonieters: on 12 occasions, between 40. and 50 kilometmeis; on 3 occasions, between 50 ancl 60 kilo- niet,ers: on 3, bet.ween 60 and 70 kilometers; on 3, be- tween i O and SO kilonieters; on l , between SO and90 kilo- met.ers: and filially on 3 occasions over 100 kilometers. I t is of int.erest to inquire what the masinium distance is, to which t.huntler coulcl be heard under t.he most favorable condit.ions, but t.liis questmion is dependent upon so many estraneous influences that it is difficult to answer. The author is led, however, to sis conclusions, regarding the long distance auclibi1it.y of thunder:
1. The loudest, t.hunder comes from t,he strongest ancl bright,est, and downwnrcl-directed li hting.
3. The intensity of the sound an % the degree of quiet surrounding t,he observer are strongly influential. 3. The evcriing a.nd night hours appear more favorable for the propngut.ion of somid than the clay hours.
4. The wiiicl direct.ion, at least up to the cloud level,
nppcnrs to have no influence. 5. In late suninier niicl aut.umii, tlie audibility condi- t.ioiis n.re much more favorable than in spring and early summer.
6. The sudibility of t.hunder is diminished by irregu- lari ties and turbulence in the atmosphere. N(.~E.-C. J. P. Cme, in Nature (.London), October 16,
1919, notes cases where the time intervnl between flash arid thundcr wits 130 seconds, 170 seconds, and lS9
seconds, yielding n ninsimum distance of 63 kilometers. Cltpt. Ault,, master of the C'ulriegk, has noted, in connec- tion wit.li t,lie sudibility of thunder at sea, that when successive intervals between li htniiig flash and thunder
inaudible when the distance of the storm esceeded 5 milcs (Sci. Amer., May 30, 1916, p. 535).--C. L. Y.
are recorded for a number of I ashes, the storm became
ANOTHER CASE.
On October 16, 1919, at 5:43 and. 594 11. m. (75th meridisn t,inie), looking northward from Chevy Chase, D. C., I observed two tremendous vcrtical lightning flaslies reawhing appareri t,ly from the overflow mam- milated to, cloud sheet of the thunderstorm. Brief
and 132 seconds, res ect.ively, indicating distances of 47 growls of t J iundcr (the only ones heard) followed in 140
and 44 kilometers; t Is le wind was moderate, southwest.
- l'. F. SPOO~S.
THE VISIBILITY OF SOUND WAVES.
.By P R A ~~K A. PERRET.
[Abstracted Irom L'Asfronomic,, Mag. 1819, pp. 193-196.]
Several instances are described in wllich the sound
w"nvcs emanating from terrific explosions in volcmoes hare nctually been macle visible by variations in the refraction of light through them. The following ex- plttiintioii is given: "* * * The sound is propagated m the air by means of compression and rarefaction
WAV~S, projected radially. The conditions for the pro- duction of these arcs are sudden explosions of great magnitude. If t.hey tire sufficiently violent, one can inie inc that the waves of ra,rt.fnct,ion and condensation wou P cl change the. indices of refract,ion a d reflection,
ttiicl these zones would be risible by contrast. The visibility by contrast of zones of cold and warm air is well known, and we ca.11 easily conceive of an analogous