18 



Tribune Extras Lecture and Letter Series. 



Syslcme faillondc), (Book IV.. chapter 10, conclusion: 

 We may fairly inquire whether this has not been the 

 case with all the satellites and their common expe- 

 rience. 



THE LAWS OF STORMS. 



BY PEOF. ELIA3 LOOMIS. 



This moraoir \vas entitled Results Derived 



from an Exainjn;,tion of tho United States Weather 

 Maps for 1S72 and 1873. It was a continuation of the re- 

 searches concerning: which Prof. Loomis presented a 

 memoir at the Academy's meeting last October, -which 

 -was at that time reported in THE TRIBUNE. The mate- 

 rial emp'.oycd in these investigations is the United 

 States weather maps for the years above named, one 

 map daily at 7J a. m. being selected. The method em- 

 pi, .yoi is tii plot out the lino of storms on skeleton maps 

 month by uionih, reduce the paths to tabular forms by 

 means of a protractor, measuring with reference to a 

 meridian, ami thus ascertain the progress of each storm 

 on a scale of inches. Reduced thus to tabular form, the 

 highest velocity is fouud in February, 31 mUes per 

 hour; the lowest in August, 17.7 miles per hour; the 

 average for the year, 25.0 miles per hour. The average 

 direction of thu slorin paths for the year is N. 82 E., 

 and is found to toe 33 more northerly in October than in 

 Julv; the vd-c:ty iu February is 75 per cent greater 

 than iu August. 



The diversity of the direction end velocity of particu- 

 lar storm* i:mrh exceeds these averages. Ou Oct. 20, 

 187U. a storm traveled N. 44 W. ; on Oct. 25, 1872, N. 18 

 W. ; on May 1C, 1873, N. 160 E., or S. E., showing ft 

 ranee of storm paths of over 180. The velocities have a 

 range from to 57.5 miles per hour. As the mean values 

 of the storm paths would thus form a very uncertain 

 guide in predicting their velocity and direction, Prof. 

 Loomis undertook an investigation or the disturbances 

 accompanying the storms, using the material afforded 

 by the weather maps. There seems to be a direct con- 

 nection between the fall of rain and tho course of a 

 etortn path. The rainfall of each storm was therefore 

 collated, and the distance on each side of the path to 

 which the rain extended. The whole number of storm 

 paths was then divided into four classes, according to 

 their respective velocities, with the following results in 

 152 cases : 



Velocity in miles Extent of rain Velocity in miles Extent of rain 

 per bom, area in miles. i" 1 ' ur. area in miles. 



3S.8 500 21.0 "<W 



28.5 543 14. r> ^05 



These numbers indicate that the rain area generally 

 extends 500 miles eastward of the storm center; that 

 When tbe rain area exceeds that extent tho storm ad- 

 vances with a vlocity greater than the mean, and when 

 the rain a;., M -i less, the velocity is below the mean. 

 The comparative acceleration or diminution of velocity 

 can be deum n! from the table. 



A similar das - <>f comparisons to ascertain the connec- 

 tion of rainfall with the direction of the storm gave the 

 following re.- ults: 



CourBp of the Storm. Ails of rnin area. 



N i.) !:. N. f>:r K. 



.-.. i n; K. N. iis 3 K. 



Tho average course of tho storm paths for 24 hours co- 

 Inci.lcs vi-r.v closely with tho portion ot the axis of the, 

 ram and tor the preceding eight hours. 



By divi ling the paths of 79 storms into quadrants tbo 

 following table of the prevailing winds was obtained : 



Velocity o f wind in 

 W. a 



I'.'" 



storms and prevailing -winds, the following result was 

 determined: 



Velocity of -torra in Velocity of win 1 in 



mile- tier hour. E. quadrant. 



3-J1 8.8 



18.1 7.8 li.3 



These numbers show that the stronger the wind on 

 tho west side of the storm, the less is the velocity of the 

 storm's progress. When the velocity iu the oast quad- 

 rant is equal to that iu the west quadrant, tho vdocity 

 of the storm is seven miles greater than the mean ; but 

 when the velocity of the wind in the west quadrant ex- 

 ceeds that in the east by 45 p-r cent, the velocity of the 

 storm's progress is seven miles per hour less than the 

 mean. 



A comparison of barometric observations showed that 

 when the barometer after a storm has passed rises 50 

 p. T cent more rapidly than usual, the storm-center ad- 

 vances 21 miles per hour more rapidly than the mean ; 

 but when the mercury afterward rises 50 per cent less 

 than usual, the storm is one that has traveled 13 miles 

 per hour less than rithe mean. The barometric pressure 

 at the center of the storm does not afford an index to its 

 progress. When the barometer ris,;s rapidly as the 

 storm passes by. the pressure at the center is increasing, 

 but when at the rear of the storm the barometer rises 

 slowly, the pressure at the center is diminishing or the 

 storm is increasing in intensity. If the rise of the baro- 

 meter is 22 per cent greater than usual, 'the central 

 pressure increases one-tenth of an inch in 24 hours ; if 

 22 p^r cent less than usual, the centra! pressure decreases 

 a tenth of an inch iu 24 hours. When the winds on the 

 western quarter of a storm are stronger than those on 

 the. eastern, the storm is increasing in intensity ; the re- 

 verse is true when the winds on the eastern quarter are 

 strongest. But this rule is subject to numerous exceptions. 

 Prof. LDOIIJIS then explained the process by which he 

 applied similar computations of tho relative velocities 

 of the winds, &c., at high altitudes, such as that of the 

 Signal Service, stations at Mount Washington ; coming to 

 che conclusion that at the bight of 0,000 feet in the west- 

 ern quadrant of a storm, the velocity of the wind is more 

 than double that of tho storm. By another series of 

 computations he obtained the forms of the isobarlc 

 curves in at least 200 cases. Iu 55 per cent of the whole 

 numher of cases the major axis of the isobar exceeded 

 its minor axis by half its length; iu 30 percent the major 

 was double the minor ; iu 3 per cent the major 

 axis was at least four times tho minor. The 

 storms of tho United States are mostly of an 

 oval form, with tlie longer axis most frequently in a 

 direction about N. 40 E. About three-quarters of the 

 great storms originate in the extreme Wost. In a case 

 of which the details were particularly reviewed It 

 seemed probable that the llrst development of magni- 

 tude iu a storm began with tlio collision of moist air 

 from the Pacific Ocean against the peaks of mountains 

 fu Oregon, resulting In heavy rainfall. But the most 

 remarkable fact elicited was that the storm, once orig- 

 inated and organizi-fl, traveled over the highest moun- 

 tain ranges without indicating sensible, obstruction, 

 proceeding eastward across the whole coutiuent of 

 North America. 



. qnn'lrant 

 7.6 



8. 



E. qnndrant. 

 8.3 



W. nnmlrant. 



in 1 



By further comparisons of extremes of velocity of 



LOWER SILURIAN FOSSILS. 



1JY PROF. J. 8. N i:\VI5F.UHY OF COLUMBIA COLLEGE, 

 NEW- YORK. 



This was a memoir on tho so-called Land 



Plants ot the Lower Silurian in Ohio. In the January 

 number of The American Journal of Science Mr. Leo 

 LesQucrcui ascribes two fossilo found in tho upycr 



