252 



tion much largei^han the present. Professor H. 

 E. Gregory at the joint geographical meeting in 

 New York (April 9-10, 1915) has pointed out 

 that the Hopis who built the clifi-dwellings 

 are migratory and frequently abandon a vil- 

 lage after having lived in it some years. 

 Therefore, the numerous abandoned villages 

 do not necessarily indicate a larger population 

 and a climate more moist in the later prehis- 

 toric times. 



[N. S. Vol. XLII. No. 1077 



THUNDER AND LIGHTNING 



De. Wm. Schmidt, after many observations 

 with his thunder-recorder, finds^ that we hear 

 but little of the air vibrations produced by 

 lightning. Thunder is accompanied by irreg- 

 ular pressure changes lasting 1/40 of a second 

 or more and some only 1/75 to 1/120 of a sec- 

 ond The periods of most of the longer pres- 

 sure waves are 1/10 to 1/3 second-too long 

 for ear perception. Much of the mechanical 

 injury done where lightning strikes is prob- 

 ably due to these waves. From a distance one 

 violent wave comes first, then follow perhaps 

 two or three series of three to four heavy waves 

 each. On account of atmospheric action on 

 irregular waves the thunder becomes of more 

 or less definite pitch. Dr. Schmidt has m- 

 ferred that at the source the lightning energy 

 may be five million times as great as that of 

 the thunder it produces. 



Insurance statistics from both Canada^ and 

 the United States show the efficacy of light- 

 ning rods in keeping buildings from taking fire 

 if they are struck.^ In Ontario, taking equal 

 numbers of rodded and unrodded farm build- 

 ings, twenty times as many of the latter as of 

 the former were struck. In the United States 

 in 1912 and 1913 two hundred insurance com- 

 panies reported 1,845 buildings struck, of 

 which but et were rodded. Considering that 

 31 per cent, of all buildings insured were 

 rodded, the lightning rod efficiency is thus 93 

 per cent. Furthermore, the reports of five 



1 Monthly Weather Eev., December, 1914, pp. 

 665-671; Scientific American Supplement, March 

 13, 1915, p. 175. 



2 See Scientific American, November 28, 1914, p. 

 347, and April 3, 1915, p. 303. 



companies for a period of 13 to 25 years on 

 18,000 buildings insured, over 50 per cent, be- 

 ing rodded, showed that the average damage 

 of the struck buildings was $10 for the rodded 

 and $2,200 for the unrodded.^ 



According to the best European data, the 

 maximum period for thunderstorms is from 

 3 to 5 P.M., while the minimum falls just after 

 midnight and from 7 to 8 a.m. The month of 

 greatest frequency is June and those of least 

 are December and January.* 



Of the 4,520 fires reported on the national 

 forests in 1913, 1,571, or about 35 per cent., 

 were ascribed to lightning. 



NOTES 



An unseasonal northeast snowstorm accom- 

 panying an intense tropical cyclone visited 

 the Atlantic coast on April 2, 1915. Snow fell 

 from Georgia northward, the heaviest about 

 ten inches being recorded around Raleigh, 

 jSr. C., at the head of Chesapeake Bay, and on 

 the New England coast. The inland extent 

 was generally leas than 200 miles; in the north 

 the railroads reported Utica, N. Y., Woods- 

 ville, Vt., and Kineo, Me., as the limits. Ea- 

 leigh, N. C, seems to have suffered most, be- 

 ing without outside telegraphic communica- 

 tion for five days. In other districts traffic 

 was hampered. The snow melted very rapidly 

 and with little or no runoff, owing to the ex- 

 tremely dry conditions of the soil after an al- 

 most rainless March. Thus agriculturally this 

 snowstorm was of great value. 



On May 1 the British Meteorological Office 

 ceased issuing forecasts except to farmers. 

 This was thought necessary because the fore- 

 casts might be of value to the Germans. 



The announcement for the 1915 interna- 

 tional kite and balloon flights came from the 

 Nicholas Central Observatory at Petrograd 

 instead of from Strassburg as heretofore. 



3 See also J. Warren Smith, "Efficiency of 

 Lightning Kods," Ohio Naturalist, Columbus, O., 

 February, 1915, pp. 437-442. _ 



i J von Hann, "Neue Beitrage zur Kenntms der 

 taglichen Periods der Gewitter," Meteorologische 

 Zeitschrift, February, 1915, pp. 73-82. 



