WEATHER FORECASTS. ] 



METEOROLOGY. 



1175 



uncertain method of indication. The use of the tele- 

 graph, in assisting weather prognostications, will be 

 easily made apparent. Supposing, for instance, at a 

 central station in England say Wolverhampton 

 ims are received, respectively, from Bristol and 

 Shields, the one noting the existence of a strong S.W. 

 wind, and the other one from the N.E. It is evident, 

 that if these currents meet, the hot, moist S.W. will, on 

 coming in contact with the cold dry X.E. , be condensed ; 

 and, in some places, where the difference of the tem- 

 perature and moisture is greatest, their mutual impact 

 must cause rain. On either side of this position the 

 winds may modify each other's character ; the S.W. will 

 part with a portion of its moisture to the dry X. E. , and 

 the latter will, of course, become more hygrometric. 

 Under such conditions clouds may be formed, but rain 

 may not fall ; and thus the weather may promise a change, 

 wlMlst none of importance immediately occurs. It will 

 thus be evident that the rain-tract, produced from causes 

 just mentioned, may be surrounded with another, in 

 which the moisture is not precipitated. By extending 

 the same reasoning for the wholu of our country, after 

 being in full possession, by telegraphic reports, at the 

 same moment, of the actual direction of the winds, their 

 temperature and moisture, and remembering that our 

 storms are usually of a cyclonic character it will be plain, 

 to the most unpractised observer, that forecasts may bo 

 made with every probability of a successful result, 

 provided that the reports furnished afford data of all the 

 various circumstances, on which, as we have already 

 shown, the occurrence of the phenomena depend. With 

 respect to the method of observing barometric and 

 tliermomctric changes, in combination with each other, 

 the reader will find a tal>lo of temperature averages at a 

 previous page, which will guide him for each mouth, in 

 the course of the year.* 



Few persons, without carefully reflecting, can gain an 

 adequate idua of the multitude of minor occurrence!), 

 which, unheeded in most cases, give warning of im- 

 pending atmospheric changes. The indications to which 

 we are about to refer, depend mostly on tho increase or 

 decrease of atmospheric moisture. Thus, the long ribbon 

 sen-weed becomes damp as moist weather approaches ; so 

 docs common salt, to a slight extent : the painted walls 

 of our apartmenU, and the iron rails in the garden, like- 

 wise become moist, for precisely the same reason as does 

 the wot bulb of the hygromotert namely, the deposi- 

 tion of moisture from the heated air on a cooler surface. 

 Stairs creak or aro quiet as the hygrometric state of the 

 atmosphere varies. With a dry" wind, the back of tho 

 cat ati'ords bright electric sparks when stroked ; but none 

 v. dim the air is moist, because tho damp conducts away 

 tho electricity. The approach of the S.W. wind, in 

 winter, after a cold N.E. wind, is immediately indicated 

 by the i/aving of our streets, and the tiles and slates of 

 our roots becoming moist ; our window-frames and doors 

 "stick" for similar reasons ; ropes, loosely stretched, be- 

 come tight, owing to the absorption of moisture, and the 

 consequent contraction of their fibres : hence, tho fre- 

 <[uciit annoyance to the housewife from the sudden 

 break-down of the posts, between which clothes have 

 boon hung out to dry. The steam from tho locomotive 

 blast-pipe seems abundant in tin; moist air on a damp 

 day ; whilst in lino dry weather it is scarcely risible, 

 bein;,' rapidly absorbed by tho surrounding air ; and, for 

 similar reasons, any wet article hung out in damp weather, 

 dries but slowly, because the air already surcharged with 

 moisture can absorb no more. Our space does not 

 permit us to enlarge on these interesting subjects ; and 

 we have only suggested the above as instances of which 

 almost every one has some knowledge, and frequently use, 

 who have any pretension to tho name of what is com- 

 monly termed a woathor-prophet. 



In concluding theso remarks on the laws of storms, 

 &c., we cannot do better than transfer to our pages tho 

 "resulting impressions" which Admiral Fitzroy affords. 

 They are as follows : 



1. Tho gyratory movements of wind, usually called 

 See unit, p. 1172. + tot n<, p. 1148. 



cyclones, are consequences of the meeting of great air- 

 currents. 



2. When so caused, in any part of the world, they 

 rotate, as eddies, during a certain time more or less 

 limited ; not exceeding four complete days and nights 

 without interruption, but usually for a much shorter 

 period. 



3. That cyclones originate on one side of tho Atlantic, 

 and traverse to the other, is a fallacy, which has arisen 

 from an insufficiency of facts, and consequent erroneous 

 combination of the details of various successive gyrations, 

 since proved to be frequent. 



4. When such an atmospheric combination happens, it 

 is not usually an isolated occurrence, but one of many 

 such, similar in nature and origin, though unequal in 

 extent, duration, and force ; not taking place at exactly 

 the same time, necessarily, but prevalent in a certain 

 zone or region of tho world during a few days or weeks, 

 or a season. 



6. The conflicting action of two currents, opposed in 

 much peculiarity as well as in direction (a feature con- 

 nected with electricity?), not only originates, a cyclono, 

 but tends to continue its striking qualities, of a wet 

 warm side and a dry cold one, owing to the continued 

 access and addition of air from each of the currents 

 (between which it is the eddy), as place is made by 

 immense precipitation of vapour in rain, hail, or snow, 

 supplied from tho vaporous side as speedily as precipi- 

 tated, or absorbed by the chilling and drying influence 

 of the antagonistic current from a polar direction. 



C. These cyclones, originating in opposition of currents 

 otherwise caused, are different from local whirlwinds, 

 occasioned by rarefaction or by electrical action, as in tho 

 sand-columns of the desert, and water-spouts. 



7. When opposing currents meet, their mosses must 

 continue in motion a certain time, either rotating 

 or ascending, or going onward horizontally, in combi- 

 nation. 



B. Mmsei of air, either of polar or tropical origin (so 

 to speak), returning, when driven back by stronger 

 opposition, at first, and for a certain time, retain the 

 characteristics of their peculiar and very different 

 natures. 



9. During the prevalence of northerly (polar) currents 

 of aii. .ty, positive or plus, is moro active or 



developed. On the contrary, with a southerly (tropical) 

 current there is no such action, no electricity in excess, 

 no positive or plus, and but little, if any, of negative or 

 minus free electricity. 



This rentmi of the, at present ascertained, laws on 

 which the system of forecasts is founded, will enable the 

 student to arrive at some general idea of the insight 

 which we now possess into those previously hidden laws 

 by which, so far as we can now judge, so many atmo- 

 spheric phenomena are governed. It must be admitted 

 that our knowledge is still extremely limited, chiefly 

 because our means of observation aro confined to within 

 so short a distance from the surface of the earth. In a 

 subsequent portion of this chapter, wo shall give an 

 account of many interesting particulars which have been 

 arrived at by means of balloon ascents, undertaken at 

 the instance and expense of the British Association, by 

 Mr. Glaishcr. Perhaps, to a certain extent, the pro- 

 ceding remarks and deduced laws may bo modified by 

 tho result* that Mr. Glaisher has obtained, and which 

 certainly do not encourage, at first sight, that assumption 

 of regular current forces to which we have so frequently 

 alluded. It must be borne in mind, however, that at 

 tho utmost height which has been attained by the 

 balloon, tho observers have barely been beyond tho 

 sphere of action of purely local causes. Hence, the 

 results necessarily cannot be relied on as bases on wliich 

 to build a safe theoretical superstructure. Repeated 

 observations, under constantly varying circumstances, 

 will bo needful, before we can safoly trust ourselves to 

 an unreserved acknowledgment of the truth of many 

 : deductions hitherto made. In every branch of philoso- 

 | phical investigations, dependent on experiment, it is 

 I safer to doubt than hastily to credit ; but in meteorology, 



