518 



SCIENCE. 



[Vol. V., No. 125. 



shows the crack in the stone in the next lower 

 course. 



Col. T. L. Casey, U.S.A., the engineer in 

 charge of the construction of the monument, 

 requested Professors Rowland of Baltimore, 

 Newcomb of the U. S. navy, and Mendenhall 

 of the signal-service, to examine the monu- 

 ment, and recommend such additions to the 

 present arrangements for protection from light- 

 ning as would seem to them necessary 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 having received the stroke. 

 A careful examination of the tip of the 

 aluminum apex has not yet been made ; but it 



seems iikety 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 

 in diameter. From 



\ l11 "™™ 



\ the end < 



\ copper 



rods, each 

 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 on 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 

 rupture 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 could possibly 

 occur, and no evidence appears of any weak- 

 ness in this respect ; but it is evident that 

 the aluminum apex alone does not possess suf- 

 ficient collective or distributing power, and 

 the improvements suggested by the committee 

 will doubtless be in the direction of increasing 

 that power by the addition of more metal. 



M. 



Washington, D.C., June 15. 



THE PERIODICAL CICADA.* 



Just at this time considerable interest is 

 manifested in this curious insect, because of 

 the concurrence of two extensive broods, the 

 one belonging to the typical septendecim form, 

 the other to the tredecim race. These two 

 broods appeared simultaneously in 1664, and 

 will not concur again till the year 2106. The 

 following are the localities in which these two 

 broods will respectively occur : — 



Tredecim (1872, 1885). 



Illinois. — Jackson, Union, Macoupin coun- 

 ties. 



Missouri. — St. Louis, Boone counties. 



Georgia. — DeKalb, Gwinnett, Newton 

 counties. 



Tennessee. — Madison county, and northern 

 portion of the state. 



Mississippi. — Copiah county, Oxford, and 

 eastern portion of the state. 



Louisiana. — Carroll Parish. 



Kansas. — Phillips county. 



Arkansas. — Flat Baj'ou. 



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, Georgia, 

 and perhaps Louisiana, require further con- 

 firmation this year. 



Septendecim (1868, 1885). 



New York. — Kings, Monroe counties. 



Massachusetts. — Fall River, south-east por- 

 tion of the state. 



Vermont. — Rutland. 



Pennsylvania. — Lancaster. 



Ohio. — Green, Franklin, Columbiana, Pike, 

 Miami counties, and vicinity of Toledo. 



Indiana. — Tippecanoe, Delaware, Vigo, 

 Switzerland, Hendrick, Marion, Dearborn, 

 Wayne, Floyd, Jefferson counties. 



Michigan. — South-eastern portion. 



Delaware. — Very generally. 



Maryland. — Very generally. 



District of Columbia. — Very generally. 



Virginia, — Very generall} 7 . 



Kentucky. — Around Louisville. 



Georgia. — Habersham county. 



From chronological data, the fact that seven- 

 teen years or thirteen years are respectively 

 required for the underground development of 

 this insect, according to the race, is fully estab- 

 lished, one of the first recorded septendecim 

 broods having been observed every seventeen 

 years since 1715. Such anomalous and excep- 



i Extracts from a paper read to the Biological society of 

 Washington, May 30. 



