them; and, therefore, that a just theory of winds, whenever it shall be formed, will be found to rest upon chemical principles, there is much reason to believe. But though little has been done in anemology, in the way of scientific reasoning, much has been accomplished, during the period under review, in the way of patient observation, and the establishment of numerous important facts. For these we are chiefly indebted to Dr. HALLEY, M. DE LA BAILLE, M. PREVOST, M. DE LA COtte, Mr. DALTON, and several of the distinguished meteorologists before mentioned, especially M. DE LUC, and Mr. KIRWAN. To these may be added Dr. FRANKLIN, Dr. MADISON, Dr. CUTler, and several other American gentlemen, who have made and recorded valuable observations on the winds in America; and a long catalogue of modern navigators and travellers, who have contributed rich materials, brought from the most distant parts of the globe, toward forming a systematic view of anemology.

Besides the great meteorologists whose names have been already mentioned, very important services have been rendered to this branch of natural history, by BOUGUER, DU CARLA, HALES, WARGENTIN, MARIOTTE, REYER, TOALDO, PRIESTLEY, and many others, to whom due honour is given by various writers on the subject. The volumes of memoirs published by the scientific academies, in different parts of Europe, during the century under review, contain rich treasures of meteorological information, contributed by numerous hands.

f Sur les Limites des Vents Alizes.

g Meteorological Observations, 8vo. 1793.

b For the observations of the above-named American gentlemen, and several others, see FRANKLIN's Philosophical Letters, and the volumes of Transactions which have been published by the American Philosophical So ciety, and the American Academy of Arts and Sciences.

i For some ingenious remarks on anemology, sec Botanic Garden, addig tional notes.

Modern times have given birth to various inventions for measuring the force and velocity of winds. Among these the most remarkable are the Wind-gage, the Anemoscope, and the Anemometer; in the construction and improvement of which Dr. LINN, Mr. PICKERING, and others, have rendered important service to meteorology. Numerous attempts have also been made, during the period under review, to construct hygrometers, or instruments for indicating the comparative states of the atmosphere, with respect to moisture and dryness. And though much imperfection is found to attend every instrument hitherto devised for this purpose, yet gradual approximations have been made toward those of a more perfect and useful kind. Among these Mr. SMEATON's hygrometer, formed of an hempen cord, boiled in salt water; M. DE SAUSSURE's, made of hair, prepared by maceration in alkaline ley; Mr. COVENTRY'S, consisting of dryed paper; and M. DE Luc's, of ivory and whalebone, deserve to be distinguished; especially that formed of whalebone by M. DE LUC, which is generally considered as the most accurate and convenient hygrometer now in use.

That remarkable meteorological phenomenon, usually called the Aurora Borealis, appeared with peculiar frequency, in the course of the eighteenth century. Dr. HALLEY tells us that it was seen but once in the seventeenth century, viz. in 1621, when it attracted considerable attention, particularly in France, where the celebrated GASSENDI observed it, and gave it the name which it now bears. After this there is no record of any such appearance until 1707, when a small one was seen. But in 1716 an uncommonly brilliant one appeared, which commanded universal attention, and was

Philosophical Transactions, No, 347.

considered by the vulgar as a most portentous event. Since that time these, meteoric phenomena have been so frequent and familiar, that they have, in a great measure, ceased to attract attention, or to be recorded as remarkable events.

Modern philosophers have ascertained many facts with respect to the Aurora Borealis, which were, of course, unknown to those who lived in the seventeenth century, and probably to all who lived before them. It seems now to be generally considered either as an electrical phenomenon, or produced by the combustion of inflammable air, either with or without the intervention of the electric spark. For the observations which have been made upon this kind of meteor, and the principles with respect to it which appear to be established, we are under particular obligations to Dr. HALLEY, M. MAIRAN, Signor BECCARIA, Dr. FRANKLIN, Dr. FORSTER, M. GMELIN, M. ÆPINUS, Dr. HAMILTON, of Dublin, Mr. CANTON, Dr. BlagDEN, Mr. DALTON, and others. The last named gentleman is supposed to have given the most satisfactory account of the subject.

HYDROLOGY,

The natural history of Waters holds so important a place among the objects of human knowledge, that it has, in almost every age, attracted the attention of those who loved to study nature: but it is only within the century under review that any thing on this subject, deserving the name of science, or a correct acquaintance with principles, could be said to exist. The accessions to Hydrology in modern times have been very great. The improvements in Chemistry, in Mineralogy, many other sciences, have contributed much

and in

to enlarge our knowledge in this department of philosophy.

The discovery of the composition of water was mentioned in a former chapter. The great augmentation of our knowledge, with respect to the doctrines of tides, during the period under review, was also noticed in a preceding division of this work. To repeat what has been said on these and some other subjects before discussed, and which might, with propriety, be introduced under this head, is altogether unnecessary.

pur

But among the discoveries and improvements of the last age, which belong to this head, the most important are the numerous and very useful investigations of Mineral Waters, which have been pursued with great success during this period. It is evident that our knowledge of the properties and effects of mineral waters must, in general, keep pace with the progress of chemical science; for which reason the early writers on this subject were, in a great measure, destitute of the best means of suing their inquiries. The publications, therefore, of Drs. ALLEN, SHORT, RUTTY, HILLARY, SHAW, and others, of Great-Britain, who wrote on mineral waters early in the century; and of many cotemporary writers on the continent of Europe, who undertook to treat of the same subject, are of little value at the present day, excepting so far as they exhibit facts. But when the sciences of Chemistry and Mineralogy reached that stage of improvement which they attained in the hands of SCHEELE and BERGMAN, the analysis of mineral waters began to be pursued upon a new and improved plan. BERGMAN, in particular, about the year 1779, wrote very ably on this subject, and gave new and instructive views of it. About the same time, Messrs. MONNET and CORNETTE, of France, and GIAONNETTI, of Italy, displayed in

their respective works, considerable talents as hy dro-analysts, and gave much valuable information to the world. These were followed by the excellent treatises of FOURCROY, on the waters of Enghien; of KLAHROTH, on the waters of Carlsbad; and of BLACK, on the waters of Iceland. In the experiments of these distinguished philosophers new and more accurate tests are exhibited; several improvements in the application of those before known are communicated; and methods unfolded of determining with precision the separate quantities of inseparable substances. Next appeared the publications of Drs. PEARSON and GARNET, and Mr. LAMBE, of Great-Britain, who, with great accuracy, analysed some of the mineral waters of their own country, and gave important information respecting them. In the same branches of mineralogical inquiry, the works of GREN, WESTRUMB, and KIRWAN, are also exceedingly valuable; especially that of the last-named gentlemen, who, in a tract singularly comprehensive, and abounding with instruction, has given a rich amount of principle, experiment, and authority, on this interesting subject. The respectable publications of Drs. MUNRO, FALCONER, and SAUNDERS, are also entitled to notice, in recounting the names of those who have thrown light on the in quiry concerning mineral waters. By the labours of these, and many other philosophers, discoveries have been made, concerning the composition and medical powers of mineral waters, in almost every part of the world, extremely useful to the interests both of science and humanity.

k Essay on the Analysis of Mineral Waters, by RICHARD KIRWAN, Esq F. R. S. &c. 8vo. 1799.