Page:Science vol. 5.djvu/554

 Q the stone id the next lower

��shows tluf crack course.

Col. T. L. Casey, U.S.A., the engineer in charge of the construction of the inuniimeDl, requested Professors Rowlnnfl of Bnltimore, Newcomb of llie U, S. navy, uad McudeDhall of the signal-service, to examiae the monu- ment, and recouiRiGud such additions tu the present arrange meats for protection from light- ning as would seem to them necessnrj and sufficient. It was ascertained on examina- tion, that, with the exception of that shown in the sketch, the monument showed no evi- dence whatever of haWng received tlie stroke. A careful examination of the tip of the ftliiminum apex haa not yet been made ; but it seems likely that it will be found to be somewhat blunted by fusion, as is so often the case even where no other effect of the stroke is to be seen. This aluminum pyramid is secured to the capstone by a heavy copper bolt one and a half inches 1 diameter. From this, four

three-quarters of an inch in diameter, are carried to the extremities of four heavy iron columns extending to the base of the monument, inside of which the elevator runs. As originally put in, these rods are bent out towards the four corners of the pyramid near which they run ou their way to these iron columns. Just where one of these is nearest to the angle of the pyramid, and hence nearest to the outside of the structure, the ruptnre occurred ; and to this must doubtless be attributed the localization of the stroke.

The damage done to the monument is in reality very small, and can easily be repaired ; but the accident is exceedingly instructive to those interested in lightning protection. The conducting power of the interior seems to be ample for any discharge which cotild possibly occur, and no evidence appears of any weak- ness ill this respect ; but it is evident that the alitrainum apex alone does not ]x>s8e8S suf- ficient collective or distributing power, and the improvements suggested by the committee will doubtless be in the direction of increasing

���\in diameter. I the end of this, copper rods.

��n county, anti northern

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lierti

��that power by the addition of more metal.

��M.

��THE PERIODICAL CICADA.'

JrsT at Ibis time considerable interest is manifested in this curious insect, becatise of the concurrence of two extensive broods, the oue belonging to the typical septendecim form, the other to the tretlecira race. These two broods api>earcd simultaneously in 1664, ftnd will not concur again till the year 2106. The following are the localities in which these 1 broods will respectively occur : — Tkedecim (1872, 1885).

Illinois. — .TacksoQ, Union, Macoupin ties.

Mismuri. — St. Louis, Boone counties

Oeorgia. — DeKalb, (Iwinneli, Ni counties.

Tennessee. — Mmlisi portion of the stale.

Mississippi. — Copiah county, Oxford, ) eastern portion of the state.

Louisiana. — Carioll Parish.

Kansas. — Phillips county.

Arkansas. — Flat Bayou.

The existence of this brood has been verified in past years in the parts of Illinois, Missouri, Tennessee, Mississippi, and Arkansas, indi- cated ) but the localities in Kansas, Geoi^ia, and perhaps Louisiana, require furlher con- firmation this year.

Septesdecih (1808, 1885).

Jfew Tork. — Kings, Monroe counlioe.

Massachusetts. — Fall River, south-east por» tion of the state.

Vermont. — Rutland.

Pennsylvania. — Lancaster.

Ohio. ~ Green, Frankhn, Columbiana. Miami counties, and vicinity of Toledo.

Indiana. — Tippecanoe, Delaware, Switzerland, Hendrick, Marion, Deai Wayne, Floyd, Jefferson counties.

Mieliigan. — South-easlorn ijorlion,

Delaware. — Very generally.

Maryland. — Very generally.

District of Columbia. — Very generally,

Virginia. — Very generally.

Kentacky. — Around Louisville.

Georgia. — Habersham county.

From chronological data, the fact that teen years or thirteen years are rcspeeti' required for the underground development this insect, according to the race, is full3- lished, one of the 6rst recorded septenfleclin broods having been observed every sevenlMii years since 1715. Such anomalous and excep-

I EiCracli fium ( paper nwl to Itie t1)olo«lat (ucIfIx af

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