August 9, 



1888] 



NA TURE 



359 



Mr. Meldrum's rules ; and the author then develops certain 

 explanations, which have been partially given by Meldrum, adds 

 slightly to the rules for handling ships, and correlates the whole 

 with the modern methods of meteorology. 



As an example, a hurricane is taken which blew near Mau- 

 ritius on February 11, 12, and 13, 1861, and the history of 

 every ship to which the rules might apply is minutely investi- 

 gated. The result, dividing Meldrum's rules shortly into three 

 parts, is as follows : — 



Rule 1. Lie to with increasing south-east wind till the baro- 

 meter has fallen 6-ioths of an inch. Seven cases, lule right in 

 every case. 



Rule 2. Run to north-west when the barometer has fallen 

 6-ioths of an inch. Three cases, two failures, one success. 



Rule 3. Lie to with increasing north-east or east wind, and a 

 falling barometer. Seven cases, rule right in every instance. 



Rule 2 was exceptionally unfortunate in this case, as the path 

 of the central vortex moved in a very uncommon and irregular 

 manner. At the same time, in any case, it appears to be about 

 equally hazardous to follow this rule or to remain hove to. 



The following new statements are then examined in detail : — 



The shape of all hurricanes is usually oval, not circular. An 

 elaborate examination is made of hurricanes on 60 different days, 

 in 18 different tropical cyclones in various parts of the world, 

 with the following results : — 



(1) Out of 60 days, cyclones were apparently circular on only 

 four occasions, and then the materials are very scanty. 



(2) The shape was oval on the remaining 56 days, but the 

 ratio of the longer and shorter diameter of the ovals very rarely 

 exceeded 2 to 1. 



(3) The centres of the cyclones were usually displaced towards 

 some one side. No rule can be laid down for the direction of 

 displacement, and in fact the direction varies during the pro- 

 gress of the same cyclone. The core of a hurricane is nearly as 

 oval as any other portion. 



(4) The longer diameter of the ovals may lie at any angle 

 with reference to the path of the cyclone ; but a considerable 

 proportion lie nearly in the same line as the direction of the 

 path. 



(5) The association of wind with the oval form is such that 

 the direction of the wind is usually more or less along the iso- 

 bars, and more or less incurved. This is the almost invariable 

 relation of wind to isobars all over the world. 



From an examination of the whole it is proved conclusively 

 that no rule is possible for determining more than approximately 

 the position of the central vortex of a cyclone by any observa- 

 tions at a single station. 



The relation of a hurricane to the south-east traie is then 

 discussed, and it is shown that there is always what may be 

 called " a belt of intensified trade wind " on the southern side of 

 a cyclone, while the hurricane is mjving westwards. In this 

 belt a ship experiences increasing south-east winds and squalls 

 of rain, with a falling barometer, but is not within the true storm 

 field. The difficulties and uncertainties as to handling a ship in 

 this belt are greatly increased by the facts that the longer diame- 

 ter of the oval form of the cyclones usually lies east and west, 

 and that there is no means of telling towards which side of the 

 oval the vortex is displaced. 



The greater incurvature of the wind in rear than in front of 

 hurricanes in the Southern Indian Ocean is next considered, and 

 then facts are collected from other hurricane countries confirma- 

 tory of Meldrum's rules for the Mauritius. 



Knipping and Doberck in the China Seas find little incurva- 

 ture of the wind in front, but much in rear of typhoons. 



Mr. Willson finds in the Bay of Bengal that north-east winds 

 prevail over many degrees of longitude to the north, i.e. in front 

 a cyclone ; and this is analogous to the belt of intensified trade 

 so characteristic of Mauritius hurricanes. 



Padre Vifiez finds at Havana that the incurvature of hurricane 

 winds is very slight in front, and very great in rear. 



The author then details further researches on the nature of 

 cyclones, which bear on the rules for handling ships. 



(1) Indications derived from the form and motion of clouds. 

 It is shown that the direction of the lower clouds is usually more 

 nearly eight points from the bearing of the vortex than the sur- 

 face wind ; but as the direction varies with the height of the 

 clouds, and as this height can only be estimated, this fact is not 

 of much value. 



(2) Looking at the vertical succession of wind currents, if the 

 march of the upper clouds over the south-east trade is more from 



the east, then the cyclone will pass to the north of the observer : 

 but if the upper clouds move more from the south than the 

 surface wind, then the hurricane will pass to the south of the 

 observer. 



(3) As to the form and position of clouds : so soon as the 

 upper regions commence to be covered, the direction in which 

 the cirrus veil is densest gives approximately the bearing of the 

 vortex. Later on, the characteristic cloud bank of the hurricane 

 appears, and the greatest and heaviest mass of the bank will 

 appear sensibly in the direction of the vortex. 



The irregular motion of the centre of a cyclone is next dis- 

 cussed, and it is shown that the centre often twists and sways 

 about, in some cases even describing a small loop. 



From this and other facts it is shown that the attempts which 

 have been made — 



(1) To estimate the track of a cyclone by projection. 



(2) To estimate the distance of a ship from the vortex, either 

 by taking into account the entire absolute fall, or by noting the 

 rate of fall, can lead to no useful result. 



A series of revised rules for handling ships in hurricanes is 

 given. Comparing these with the older oms it will be 

 remarked — 



(1) That the rule for finding approximately the bearing of the 

 vortex is slightly modified. 



(2) That the great rules of the "laying to" tacks remain 

 unaltered. 



(3) That the greatest improvement is the recognition of the 

 position and nature of the belt of intensified trade wind on the 

 dangerous side of a hurricane, where a ship experiences increas- 

 ing wind, without change of direction, and a falling barometer. 

 The old idea that such conditions show that a vessel is their 

 necessarily exactly on the line of advance of a hurricane is- 

 erroneous. She may, but she need not be ; and under no cir- 

 cumstances should she run till the barometer has fallen at least 

 6-ioths of an inch. 



(4) There are certain rules which hold for all hurricanes ; but 

 every district has a special series, due to its own local peculiari- 

 ties. Those for the South Indian Ocean are given in this- 

 paper. 



Paris. 



Academy of Sciences, July 23. — M. Janssen, President,, 

 in the chair. — The President announced the death, on July 19, 

 of M. H. Debray, member of the Section of Chemistry, whose 

 name will always be remembered in connection with the laws 

 determining the tension of dissociation, the density of the vapour 

 of sulphur, and other researches throwing much light on many 

 obscure chemical phenomena. — Note on target practice, by M. 

 J. Bertrand. In continuation of his previous communication 

 (Comptes rendus of February 6, 1888), the author here shows 

 that the actual results of 1000 experimental shots correspond' 

 closely with the theory as expressed by the general equation 

 k l x*- + 2\xy + k' 1 y l = H. The practice was at a distance of 

 200 metres with ten rifles of like model, each marksman firing 

 ten shots with each rifle. — Remarks on the quantitative analysis- 

 of nitrogen in 'vegetable soil, by MM. Berthelot and G. Andre. 

 The analysis of nitrogen in ground containing nitrates presents 

 some apparent difficulty. But the results of the researches here 

 described show that in the case of ground poor in nitrates, the 

 analysis may be safely and rapidly executed with a blend of lime 

 and soda. — On the luminous bridges observed during the transits 

 and occultations of the satellites of Jupiter, by M. Ch. Andre. 

 As in the transits of Venus, these optical phenomena are here 

 shown to be entirely due to the optical surfaces of the instruments 

 modifying the direction of the luminous waves. They are, in 

 fact, a result of diffraction in the instruments of observation. — 

 Measurement of the coefficients of thermic conductibility for 

 metals, by M. Alphonse Berget. The author here applies to red 

 copper, brass, and iron, the same method he has already adopted' 

 for mercury (Comptes rendus, July 25, 1887, and July 16, 1888), 

 with the following results : red copper, h = 1 0405 ; brass, 

 k — 0*2625 ; iron, k = 0*1587. — Magnetic determinations in the 

 basin of the West Mediterranean, by M. Th. Moureaux. Having 

 been charged by the Minister of Public Instruction to collect the 

 elements needed for the preparation of magnetic charts for this 

 region, the author obtained in the period from April 19 to June 

 25, 1887, as many as ninety measures of declination and fifty- 

 nine of inclination for fifty-two stations. The results are here 

 tabulated for these stations, of which four are in Corsica, three 

 in Italy ; two in Malta, one in Tripoli, seven in Tunisia, twenty- 



