APPENDICES. V. Note on relation between sun pots and weather. LIST OF PLATES. (To be placed at end.) IV. Lines, showing the isabnormal temperatures of the globe in January. V. Lines, showing the isabnormal temperatures of the globe in July. VI. Map, showing the mean atmospheric pressure and prevailing winds ▸ VII. Map, showing the mean atmospheric pressure and prevailing winds VIII. Current chart of the globe for the year. IX. Isothermal lines, showing the mean sea surface temperature for X. Isothermal lines, showing the mean sea surface temperature for XI. Lines, showing the regions of equal annual range of temperature. ELEMENTARY METEOROLOGY. PART 1. CHAPTER I. INTRODUCTORY. METEOROLOGY is the science of the Atmosphere, of Tà μETέwρa, the things above the earth, as Aristotle has it, and its interest to everyone scarcely needs to be dwelt upon, for as without air we cannot live, any knowledge which we can gain of its condition from time to time, and of the changes which are taking place in it, cannot fail to be of the very highest importance to our health and comfort. Almost everyone imagines himself a born meteorologist, and from the earliest times men have been watching the weather and its changes and recording their experience thereof; in fact, the Book of Job, believed to be one of the earliest of the Biblical Canon, contains some sound meteorological knowledge, as true now as it was some three thousand years ago. Nevertheless, though men have studied meteorology more or less systematically ever since the time of B Aristotle, who wrote the first treatise on the subject, little progress was made in it until the invention of the barometer and thermometer, about 200 years ago, and we must admit that even yet it has hardly made good its title to a place among the exact sciences. The reason of this is easily explained. Firstly, we live at the bottom of the atmospheric ocean, of which the upper layers are practically inaccessible, and their condition almost unknown to us. Secondly, the observations we make of the physical state of the air are affected to such a degree by local accidents, such as the elevation, contour, and slope of the ground, its nearness to the sea, and even the character of the soil, that we meet with considerable variations of meteorological circumstances even within the limits of a single county. In this respect meteorology affords a strong contrast to astronomy. The objects of observation and study in the latter science are at such a distance from the earth that it is practically of minor importance whether they be observed from Greenwich, Rome, or Washington. The phenomena themselves are identical, and, other things being equal, the difficulties of making the observation depend mainly on the meteorological conditions of the locality. In fact, under favourable meteorological circumstances, the range of phenomena observable by an astronomer is limited solely by the horizon of his station, and the power of his telescope. But in meteorology itself the case is widely different; the phenomena are not the same at two different points of observation. To take a single element, the temperature of the air in the streets of London differs appreciably from that experienced at the same time in the middle of the parks, and à fortiori from that observed entirely outside the city, as at Kew or Greenwich. Hence we see the necessity of covering the country with a network of independent meteorological stations, as the observer at each place cannot do much more than record the phenomena exhibited by the portion of the atmosphere actually in contact with his instruments. We may exemplify the difference between the two sciences by an illustration taken from biology; the astronomer may be compared to some of the more highly organised among the mollusca, such as the octopus, which is endowed with powers of locomotion and can seek his food at a distance from his home; while the meteorologist is like a mussel or an oyster, anchored to one spot, and obliged to make the best of such nutriment as may chance to be swept within his reach. Meteorology may be considered from many different points of view. In the first instance, observations taken systematically at one place give eventually information as to the climate of that place, and when the results. obtained for one such station are combined with those for other stations and compared with those taken in other countries, deductions may be drawn bearing on the relative fitness of different localities for the support of animal and vegetable life, &c., &c. From this climatological point of view, the subject is immediately related to the science of physical geography, and in a greater or less degree to sanitary science also, and it is in this connection that it has been longest and most perseveringly studied. Secondly, meteorology may be treated as the science of weather that is of the changes which are from time to time taking place in the physical condition of the atmosphere and of the effects produced by such changes. These effects find their expression in the temperature of the air, the direction and motion of the wind, the amount of moisture contained in the atmosphere, and the balancing of the antagonistic forces of evaporation and condensation, on which depend what is termed, in common parlance, the fineness, or the contrary, of the weather. This branch of the subject has attracted much attention of late years, owing to the development of telegraphy and the facilities which are thereby afforded for examining the conditions of weather existing simultaneously at different places. We cannot, however, claim for the study of weather that it has as yet made much practical progress in enabling us to foresee or forecast its course for more than a few hours, and we must admit that it has made next to no progress at all in gaining an insight into the agencies which are at work in producing the various phases of weather. Thirdly, we have the highest object of meteorology, if we consider it as a department of cosmical physics: the investigation of the physical conditions of the atmosphere, and their relations to the forces of light, heat, electricity, and magnetism. We cannot doubt that this department of meteorology, if thoroughly followed up, will yield results of the highest interest and importance, besides throwing light on many common phenomena, which are as yet entirely unexplained. Here, however, we are at once staggered by the difficulty to which allusion has already been made. We live at the bottom of an ocean, and have no means of testing its condition above the level at which we live, |