GASEOUS RADIATION, ETC., OF HEAT.] 



METEOROLOGY. 



1191 



be sensitive, and in good order ; yet we have just seen 

 that some instruments are sold, and doubtless "war- 

 ranted," which would be incapable of showing a great 

 mercurial depression, generally the only sign of the 

 coining storm that could warn the mariner of im- 

 pending danger. There is no difficulty whatever in 

 having a good barometer properly tested ; and as our 

 knowledge of the science of storms is now so extensive, 

 the commander of a vessel would be guilty of an equally 

 great neglect of his duties and interests, if proceeding to 

 sea without a good and certified instrument, as he would 

 be were he to do so without either a compass or chrono- 

 meter on board. 



Whilst referring to methods of registering observa- 

 tions, we may observe that the Board of Trade lend 

 barometers, <kc., on certain conditions, to properly 

 qualified commanders in the merchant service. They 

 are expected to make continuous observations, and to 

 report them at head-quarters as occasion will permit ; 

 honorary rewards being distributed when the instruc- 

 tions are fully carried out, or when special diligence has 

 been shown. This plan will prove highly beneficial to 

 tbe interests of science ; for, by it, an immense amount of 

 data will be gathered from all parts of the world, and 

 thus our means of induction will b proportionately 

 increased. Besides the registration of the heights 

 of the barometer, <kc., the observers are desired to 

 notice all concomitant occurrences, go as to increase our 

 knowledge of matters which, although apparently of 

 minor importance, are really efficient aids to the more 

 exact processes of scientific investigations.* It may not 

 be unreasonable to hope, that, in the course of time, 

 simultaneous observations will be undertaken through- 

 out the world, on a plan similar to that adopted at our 

 observatories in this and other countries. The labour of 

 reducing them would, of course, be enormous ; but the 

 information obtained would be invaluable. Carried on 

 during a number of years, we might, eventually, be able to 

 form from them so complete a weather-chart for each 

 ocean and coast, as would result in a general diminution 

 of shipwrecks, which now cause, annually, some millions 

 sterling of loss. To many, such a work would seem 

 Utopian, and utterly beyond human power ; but, after 

 all, it would scarcely equal the labours of astronomers, 

 who have mapped out the place of each star, and who, 

 from data similarly acquired, can assign its place, even 

 for years hence, within an error of but a few seconds of 

 time. In this labour we are encouraged by knowing 

 that no event in nature depends on chance, and that 

 every phenomenon is the result of some law which has 

 been impressed by the Creator. In its operation, it may 

 be so intricate as to bailie, for years, and even ages, the 

 deepest penetration on our part ; but still it stands 

 before the eye of the philosopher, presented as a great 

 prize for his grasp the only condition imposed on him 

 for success being, an intelligent, persevering, and discreet 

 use of each fact as it arises, and of correct induction as 

 light bursts on his mental vision. For some thousands 

 of years, ingenuity was puzzled to account for the motions 

 of the solar system ; the most intricate schemes wore 

 brought forth to explain them ; but when human pride 

 failed, nature's simplicity conquered ; and one broad com- 

 prehensive law that of gravitation was at last under- 

 stood and completely established ; a result which ade- 

 quately rewarded years of unremitting and patient toil. 



GASEOUS RADIATION AND ABSORPTION OF HEAT, AND 

 THEI u EFFECTS ON CLIMATE. In the Section on Heat, 

 we have called attention to a variety of phenomena 

 resulting from the radiation and absorption of caloric ; 

 and in the Addenda to that section, some interesting 

 experiments and results, obtained by Professor Tyndal), 

 are briefly noticed. We shall hero extend this subject, 

 so as to point out its bearings on the science of meteor- 

 ology, in connection with climatic differences, and may 

 find that many phenomena, otherwise almost inexplicable, 

 receive a happy solution through the inductions which 

 may be properly made from the facts that will be brought 

 forward. 



See antt, p. 1177. 



Casting a glance at a map, from the poles to the 

 equator, the intelligent student will not fail to remember 

 how various is the climate of the different countries 

 delineated on it ; and, consequently, how greatly the 

 natural productions vary. Whilst experience teaches us 

 that certain forms of both animal and vegetable 

 existence are confined within definite regions or zones ; 

 that, in some places, rain, snow, frost, and hail aro 

 unknown ; whilst in others they are characteristic of the 

 country ; and, in some, that there is experienced, during 

 the day, a tropical heat, followed by an almost Arctic 

 severity of climate as soon as the night sets in we 

 naturally seek for some general law, which may embrace 

 a broad and definite exposition of the causes operating in 

 each instance ; not being content with an approximative 

 or probable solution of our inquiries. 



What an almost infinite variety exists of the evidences 

 of vitality in different portions of our globe. Com- 

 mencing at the polar regions, we find vegetation the 

 immediate characteristic of climate in its lowest forms ; 

 the lichens being predominant in all respects. Gradually 

 approaching the equator, we first see hardy plants and 

 trees, such as the willow, birch, alder, etc. ; and grass 

 also becomes common. Flowers of various kinds, with 

 cereal crops, next appear as we arrive in countries such 

 as our own ; thus tlie luxuriance of vegetable nature, 

 and its profusion, develop, until we arrive at tropical 

 regions, where the heat and moisture combine to produce 

 the richest and most gorgeous .of floral beauties, and 

 sugar, coffee, spices, fruits, &c. , which can only flourish 

 in such countries. Animal life equally sympathises with 

 the peculiarities of climate, if we confine ourselves to 

 those forms that are below the human species, to 

 which alone is accorded the power of accommodating 

 itself to every climate, no matter how severe or sudden 

 the transition. 



The general laws which influence this climatic variety 

 have been already inquired into in the previous pages ; 

 and, in numerous instances, the particular or local 

 disturbing causes have also been pointed out. There 

 are, however, other influences of both kinds, to which 

 we shall now direct attention, and which have been, till 

 lately, almost unknown, or scarcely allowed for, to the 

 extent which their importance demands. 



We may first notice the effect of the obliquity of the 

 sun's rays, as incident at various parts of the world, 

 being well aware, that where the sun is vertical, those 

 regions, as at the equator, are the hottest of any on the 

 globe. At the outer limits of the atmosphere, it is 

 considered that the area bounded north and south of the 

 equator, by the parallels of latitude of 23 45', receives 

 as much solar heat and light as does all the rest of the 

 surface of the earth. Whilst au obliquity of 25, in the 

 incidence of a solar ray, causes a loss of one-half of its 

 intensity at that angle before reaching the earth ; an 

 inclination of only 5 = permits only ifath of the maximum 

 to be transmitted to us. It hence follows, that the 

 remaining portion of our globe must, on areas equal to any 

 given one at the equator, receive an exceedingly 

 small proportion of the total calorific rays emanating 

 from the sun. 



From this we may plainly see, that the great breadth 

 of land extending between the eastern and western 

 limits of Africa, and the parallels of 23 45' north and 

 south of the equator, must act as an enormous absorber 

 of solar heat ; which it afterwards radiates, and from 

 which, by convection, the remaining portion of the earth 

 receives a great accession beyond what would be its 

 normal temperature. The upward current of hot air 

 rising from this surface, spreads itself northward and 

 southward, and its place is supplied by returning currents 

 of cold air, which, by this compensating action, and 

 influenced by the rotation of the earth, are productive 

 of the trade winds, as already pointed out in our previous 

 pages, t 



But it is evident, that unless some special provision had 

 been made for the retention of the heat thus absorbed 

 about the equatorial regions, aud subsequently carried, 



t See ante, Section on Beat, p. 30 ; and in this Section, p. 1131. 



