November, 1906 ] 



KNOWLEDGE & SCIENTIFIC NEWS. 



579 



portant of these conclusions : — (i) In travelling- storms, while 

 in the front portion there is motion of the air from higher 

 pressure to lower pressure, associated with falling tempera- 

 ture and with the gradual development of cloud and rainfall, 

 there is also in the rear, sometimes from points quite near 

 to the centre, motion of air from lower pressure to higher 

 pressure and higher temperature with improving weather, 

 and again there are instances of motion with practically no 

 change of pressure, temperature, or weather. Over the 

 .Atlantic, air moves generally from higher pressure to lower 

 pressure, but sometimes from lower pressure to higher 

 pressure. There are also instances of air moving for long 

 distances with little or no change of pressure. (2) .■Xn 

 essential difference must be drawn between fast travelling 

 storms (as estimated by the ratio of the velocity of the centre 

 to the speed of the wind) and slow travelling storms. The 

 former take all their air for the part which is represented by 

 circular isobars from the region on the right hand or 

 southern side of the path in the front of the storm and 

 throw out an approximatclv equivalent amount on the same 

 side in the rear. A slow travelling storm makes use of air 

 from both sides of its path. That from the right hand or 

 southern side flows directly towards the central portion, 

 while that from the northern side curls round the rear of 

 the storm. This difference in the characteristics of the two 

 types cannot be accounted for by regarding all approxi- 

 mately circular storms as revolving vortices of air carried 

 along by currents of different velocities. (3) Tn travelling 

 storms the veering of wind is not generally a uniform 

 sequence. Winds from some of the directions are relatively 

 transient ; on the other hand, winds from other directions 

 are relatively persistent during the passage of the storm, 

 even at considerable distances from the centre; the transi- 

 tion from the one persistent direction to the other is com- 

 paratively sudden. In fast travelling storms the directions 

 of the more persistent winds are S. or S.W. and N.W., 

 while in the case of slow travelling storms the more per- 

 sistent winds are E. to N.E. and S.W. to .S. (4) On the 

 eastern side of the .Atlantic, surface air currents from the 

 south are generally short lived, and soon disappear in the 

 central portions of cyclonic depressions. Onlv in fast 

 travelling storms do southerly currents continue beyond the 

 path of the centre and describe loops round the centre. 

 (^) Air currents from other directions than the south are 

 nnirh longer lived. They persist until cither fo) they reach 

 the trade winds, or (6) turn round the rear of a depression 

 and approach the centre from the southward, or (c) join a 

 depression over the Western .Atlantic. (6) The rainfall in- 

 cidental to travelling storms can be, generally speaking, 

 related to the asrent of air from the surface, as indicated bv 

 the convergence of the .nir, deduced from its motion, in a 

 region not far distant frimi the locality of the rainfall, 

 generally to the south or south-east of it. (7) The regions 

 of high pressure that intervene between depressions and 

 travel with them may be called anticyclones when we are 

 dealing with a chart for a restricted area, but thev are to 

 be distinguished from the well-defined anticvclones which 

 are persistent for days together. These latter are for the 

 most part inert and comparatively isolated masses of air, 

 taking little part in the circulation which goes on around 

 them. (8) The motion of air with reference to the moving 

 centre of a cyclonic depression is not, as a rule, properly 

 described as circular motion round the position of minimum 

 pressure, modified by incurvature, and transformed into 

 spiral motion about a moving centre. The description would 

 apply to the motion of air in the case of certain currents 

 commencing on the northern side of a slow travelling storm, 

 but the following cases of motion also occur : — (n) in ap- 

 proximately straight lines leading towards the minimum or 

 a point on its path in front, or on the trough line of a 



V-shaped depression, (b) round the minimum in curves, to 

 which the minimum stands rather in the relation of the 

 focus of a conic than that of the centre of a circle. 



Space does not permit us to discuss to what extent these 

 conclusions, if valid, will modify the body of conclusions 

 known as " the laws of storms," and hence the methods and 

 practice of forecasting in the English Meteorological Office. 

 In conclusion we congratulate the Meteorological Office on 

 the results of the investigation. It is an example of the 

 importance of research based on scientific methods which is 

 now essential to further large progress in the improvement 

 of the practical work of weather forecasting. 



The Carriers of Plague. 



" Pulex Cheopis. " 



.So long- has plague In India been associated with rats 

 that there is a proverb to the efTect that " when the 

 rats beg^in to fall from the rcwf, it is time for people to 

 leave the houses." The Indian rat falls from the ceil- 

 ing; cloths and mud roofs of the Indian go-downs and 

 bung'alows and huts because it is a house rat and not 

 a sewer rat like the English variety; and, consequently, 

 the incidence of an epizootic of plague among rats in 

 India is usually marked by the deaths of numbers of 

 them in and about the walls and ceilings. And gener- 

 ally this appearance of plague among the rats is 

 followed by the appearance of plague among human 

 beings. But though there seemed thus an immense 

 probability that plague among rats was transmitted to 

 human beings, there has been great difficulty in proving' 

 it, and the difficultv lay in fixing on the means of tran.s- 

 mission. This difficultv has been disposed of bv the 

 investigations of the latest scientific commission, which 

 was appointed by the Indian Government, and which 

 is still pursuing its \yDrk. So important are the results 

 of its first year's inevstigations, and so decisive are 

 thev, that they have been published as an interim re- 

 port in the "Journal of Hygiene." Thev establish 

 definitely the fact that the chief carrier of plague from 

 rat to rat, and from rat to man, is the rat flea " Pulex 

 cheopis. " 



The commission, instituted by the Indian Govern- 

 ment, at the instance of Dr. Martin, F.R.S., Director 

 of the Lister Institute, comprised Major Lamb and Cap- 

 tain Liston, of the Indian Medical Service, Dr. Petrie 

 and Mr. .Svdncv Rowland, of the Lister Institute, and 

 several Indian investigators of plague. Mr. Kasava Pai 

 among them, lent by various Indian .States. The com- 

 mission had to set about its work from the beginningf, 

 and unprejudiced by the conflicting experiences and 

 theories of preceding investigators. For, although evi- 

 dence in support of the connection between plague 

 among rats and plague among human beings has ac- 

 cumulated since the discoverv of the plague bacillus bv 

 Yersin .ind Kitasato, there have been manv negative 

 results in the attempt to demonstrate the belief posi- 

 tively. Most of the observcr.s who have studied the 

 C|uestion on the spot — ^'ersin, Ogata, Simond, Thomp- 

 son, Koch, and Gaffky — have arrived at the opinion that 

 from an epidemiolog-ical point of view plague is to be 

 regarded as a rat disease in which human l)eings mav 

 I.Mirticip.ito. The relationship of the epizootic among 

 rats and the epidemic among" human beings has been 

 particularly studied with great care for the outbreaks in 



