A WEEKLY ILLUSTRATED JOURNAL OF SCIENCE. 



" To the solid ground 

 Of Nature trusts the mind which builds for aye." — Wordsworth. 



THURSDAY, MAY 5, il 



LOOM IS' S CONTRIBUTIONS TO 

 METEOROLOGY. 

 Contributions to Meteorology. By Elias Loomis, LL.D., 

 Professor of Natural Philosophy and Astronomy in 

 Yale College, &c. Revised Edition. Chapter II. 

 (New Haven, Conn., 1887.) 



IN Chapter I. of the revised issue of these valuable 

 contributions to meteorology, Prof. Loomis sum- 

 marised, and in some directions materially extended, the 

 laborious investigations on which he had been engaged 

 for the previous ten years, with reference to areas of low 

 atmospheric pressure — their form, magnitude, direction, 

 and velocity of movement (Nature, vol. xxxiii. p. 49). 

 In Chapter II. he similarly deals with the allied problems 

 of meteorology which group themselves round areas of 

 high atmospheric pressure, investigates their form, mag- 

 nitude, direction, and velocity of movement, and con- 

 cludes by tracing some of the more important relations 

 of areas of high to areas of low atmospheric pressure. 



It is premised that areas of high pressure exhibit 

 characteristics quite unlike those which attend areas of 

 low pressure. A typical example, contrasting the two 

 sets of phenomena, is given in the great storm of 

 February 5, 1870, where, in the centre of the Atlantic, 

 pressure fell to 27*33 inches, whilst at the same time, 

 and contiguous to this great cyclone, there occurred a 

 strongly-marked anticyclone in Europe, where, over an 

 extensive region, pressure rose to upwards of 3 roc 

 inches. Near the centre of the cyclone the winds blew 

 with hurricane force, but near the centre of the anti- 

 cyclone the atmosphere was well-nigh calm. In the 

 cyclone the winds circulated about the low centre in a 

 direction contrary to the hands of a watch, with, at the 

 same time, a decided tendency inwards upon the centre 

 of low pressure ; whereas in the anticyclone the winds 

 circulated about the high centre in the same direction as 

 that of the hands of a watch, with a decided tendency 

 outwards from the centre of high pressure. 



As regards their form, cyclones nearly always approxi- 

 VOL. XXXVI. — No. 914. 



mate closely to the circular, elliptical, or oval forms ; but 

 on the other hand, the departures of anticyclones from 

 the circular form are nearly always quite palpable ; 

 indeed, we rarely find an isobar about a centre of high 

 pressure which does not clearly deviate from the figure of 

 an exact circle. The isobars are generally elongated, and 

 are thus elliptical rather than circular, and the elongation 

 is sometimes very great. 



In order to ascertain the general form of the isobars of 

 anticyclones, Prof. Loomis has examined and measured 

 with care 238 well-defined cases, shown on the United 

 States weather-maps. The result indicates that the 

 average ratio of the longest to the shortest diameter was 

 I •91. Whilst the longest diameter may be turned in any 

 direction, 72 per cent, of the cases occurred in the azi- 

 muth from 0° to 90°, the direction of maximum frequency 

 being N. 44° E. It is noteworthy that these results inti- 

 mately agree with those found for low-pressure areas, 

 showing, together with other results, how intimately 

 cyclones and anticyclones are connected. 



A similar investigation has been carried through as 

 regards these two great systems of pressure for the 

 Atlantic and Europe. In this part of the inquiry the 

 number of cases examined was 252, which showed that 

 the average ratio of the longest to the shortest diameter 

 was I "84 ; and as respects the direction of the longest 

 diameter, 69 per cent, of the cases occurred in azimuth 

 from 40° to 130", the direction of maximum frequency 

 being N. 75° E. Thus, while there is a remarkable 

 correspondence between the results for these two great 

 regions of the globe as respects the form of anti- 

 cyclonic isobars, there is not the same accord as to the 

 prevalent direction of the longest diameter. It may be 

 well to emphasise here this vital difference between the 

 anticyclones of North America, and those of the much 

 larger Europasian continent. About three-fourths of 

 these anticyclones occurred during the six colder months 

 of the year. 



When an area of high pressure is situated between two 

 areas of low pressure not far apart from each other, the 

 anticyclone generally takes a very elongated form, and 

 sometimes the isobars surrounding this high area extend 

 a distance of several thousand miles, with but little 



