NATURE 



49 



THURSDAY, NOVEMBER 19, 1SS5 



LOOMIS'S "CONTRIBUTIONS TO 

 METEOROLOGY" 



Conti-ibulions lo Meteorology. By Elias Loomis, LL.D., 

 Professor of Natural Philosophy and Astronomy in 

 Yale College, &c. Revised Edition. (New Haven, 

 Conn., U.S., 1885.) 

 T T is now fifty years since Prof. Loomis's attention was 

 directed to the study of meteorology, his interest in 

 the subject having been awakened by Redfield's investi- 

 gations respecting the phenomena and laws of storms. 

 During the first forty years his principal writings were 

 elaborate discussions of the great storm which occurred 

 in America in December 1836, and an equally remarkable 

 storm which occurred in Europe shortly after the American 

 storm, and an account of another United States storm in 

 February 1842, which in a part of its course was accom- 

 panied by a tornado of unusual violence. The chief out- 

 come of these investigations was a new method of charting 

 observations, now so familiar to all the world in our 

 weather maps, and the demonstration of the capital fact 

 in meteorology, that in storms the movement of the wind 

 is spirally inwards, circulating from right to left about the 

 centre of the cyclone. 



The generally imperfect character of the barometric 

 observations for a long time precluded all attempts at any 

 satisfactory investigation of the storms and weather of 

 the United States ; and it was not till 1871, when the 

 Signal Service was organised, with its uniform methods 

 of observation and reliable barometers, that the data 

 required for the investigation was supplied. When two 

 years' observations had accumulated, Prof. Loomis 

 resumed his inquiries, and from July 1874. a series of 

 papers by him, entitled " Contributions to Meteorology " 

 have appeared from time to time in the American Journal 

 of Science. A large number of these we have noticed in 

 Nature as they appeared. As the subjects investigated 

 were taken up without any regard to systematic order, 

 and as a change of views has necessarily come about as 

 the investigations proceeded. Prof. Loomis has wisely 

 resolved to reduce them to a more systematic form and 

 incorporate into the revised work the results of observa- 

 tions now available, not only from the United States, but 

 also from Europe and other parts of the world. The 

 present pamphlet contains the first chapter of this revision, 

 and the subject dealt with is the areas of low atmospheric 

 pressure, their form and magnitude, and the direction and 

 velocity of their movements. 



As regards the forms of areas of low pressures, or 

 cyclones as they are conveniently termed, the greatest and 

 least diameters of all the cyclones represented on the 

 Weather Maps of the Signal Service during a period of 

 three years were actually measured, with the result that 

 the average ratio of the longest diameter to the shortest 

 was I '94. In 53 per cent, of the whole number of cases 

 the ratio was r5 ; in 33 per cent. 2 ; in 1 1 per cent. 3 ; 

 and in 3 per cent. 4. Similarly the .Atlantic storms, as 

 delineated on Hoffmeyer's charts for a period of three 

 years, have been examined, and the measurements show 

 that the ratio of the longest diameter of the cyclones to 

 Vol. xxxiii. — No. 838 



the shortest is 170 ; and that while in 54 per cent, of the 

 whole number of cases the ratio was I'j, in 17 per cent, 

 it was 2, and in i per cent. 3 — thus showing a marked 

 deficiency of very elongated low pressure areas over the 

 Atlantic Ocean as compared with the United States. 



Observations show that the longest diameter of cyclones 

 may be turned in any azimuth. In the States it is most 

 frequently directed towards a point somewhat East of 

 North, the point towards which the longest diameter is 

 most frequently directed being N. 36° E. The average 

 direction is sensibly the same for the cyclones of the 

 Mississippi Valley and for those of the Atlantic coast. 

 Over the Atlantic Ocean the direction of the longest 

 diameters are more equally distributedin azimuth than they 

 are in the United States, but the point towards which the 

 longest diameter is most frequently directed is N. 35' E., 

 which corresponds almost exactly with the direction found 

 for the LTnited States. 



The cyclones of the tropics frequently exhibit a violence 

 greater than is ever known in the storms of the middle 

 latitudes, but their geographical extent is comparatively 

 small. The inclination of the winds inwards upon the 

 centre is shown to be more strongly marked in tropical 

 cyclones than in most storms of the middle latitudes. 

 From an examination of the weather maps of the Signal 

 Service it is found that in the United States a low pressure 

 area, with only one system of cyclonic winds, frequently 

 has a diameter of 1600 English miles, and Hoffmeyer's 

 charts show that cyclones over the Atlantic have 

 frequently diameters of 2000 English miles. Widespread 

 areas of low barometer, having several centres of cyclonic 

 action, may have a diameter of 6000 English miles or 

 may even form a belt extending nearly, if not entirely, 

 round the globe between the parallels of 40° and 50° N. 

 lat. On the other hand, tropical cyclones are often only 

 500 miles in diameter, and are occasionally of still less 

 dimensions. 



When low pressure areas are very much elongated, two 

 or three cyclonic centres are frequently included within 

 the same area of low pressure. Though these cyclonic 

 centres are occasionally of equal depth, yet they are more 

 generally of very unequal depth and intensity. The 

 weather charts of the morning of March 9, 1S76, showed 

 a very large area of low pressure overspreading Europe 

 and the Atlantic Ocean, having a principal centre of low 

 pressure in the north of Scotland, around which violent 

 winds prevailed, rising to 12 on Beaufort's scale, with very 

 steep gradients on the western side of the cyclone. About 

 the same time, and within the same widespread low pres- 

 sure area, there were four other cyclones, with their 

 centres at St. Petersburg, South Russia, south coasts of 

 the Black Sea, and over the Caspian Sea, respectively. 



As an illustration of one of the more extensive areas 

 of low pressure. Prof. Loomis adduces the great baro- 

 metric depression of June 7, 18S2, as shown on the 

 International Weather Map of the Signal Service of that 

 day. This area of low pressure covered the whole of 

 Asia, apparently extending from the equator to a consider- 

 able distance beyond the North Pole ; it covered the 

 whole of Europe with the exception of a small portion of 

 its southern margin, and also the northern part of the 

 Atlantic Ocean and stretched across the central portion 

 of North America to the Pacific Ocean : thus extending 



