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. EPINUS, 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, and in many other sciences, have contributed much

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.

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 pursuing 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 hydro-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 inquiry 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.

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

CHAPTER IV.

MEDICINE.

THE profession, whose department of knowledge now comes under consideration, occupy an immense field of science, and, by their number, constitute a large class of the learned world. In addition to the incentives of philanthropy and fame, which equally actuate the exertions of others, physicians are combined into a corps of observers and practical inquirers by the nature of the employment and duties they assume, and by the connection which the usages of society establish between their duties and emolument. In discharging their professional labours, they incessantly find observations and facts obtruded on their attention; and by combining these into hypotheses, theories and systems, they only indulge a favourite and almost irresistible propensity of the human mind. Hence arises the vast mass of writings which fill medical libraries, constantly accumulating, and too numerous, extensive and diversified to come within the comprehension of an individual inquirer. Whoever duly considers these things will perceive the necessity of resting satisfied on this occasion with a transient retrospect. To attempt any minuteness of detail would be to travel far beyond the limits assigned to this work, and to engross the pages which are destined to the examination of other subjects. All that can be aimed at is briefly to notice some of

the more important revolutions and improvements which distinguish the last age, and to commemorate a few of the illustrious names to whom the praise of them is chiefly due.'

Within the period assigned for this review, the state of medicine has been essentially changed, and has acquired a degree of extent, popular dissemination, and practical usefulness, unknown to preceding ages. The improvements in natural history and chemistry, mentioned in the preceding chapters, have greatly contributed to this extension, and may be considered as inexhaustible sources of materials calculated for a similar extension in future times. The more enlarged intercourse of mankind, the greater facility of communicating opinions and discoveries from one gion to another, and the progress of commercial arrangements, by which the choicest productions of one country become the property of every other, may also be enumerated among the causes of this advancement.

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In no period so much as in the last century, and in no science more than that which now engages the reader's attention, have the advantages been exhibited which arise from Lord BACON's plan of pursuing knowledge by observation, experiment, analysis and induction. Every department of medicine bears witness of the efficacy of this process to remove the rubbish of prejudice and error, to present truth in a simple form, and to establish upon a legitimate foundation. A more precise, rigid and logical mode of philosophising has been generally substituted for the wild and visionary hypotheses which disgraced the science of the preceding centuries.

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7 For many of the names, facts, and details included in this chapter, the author is indebted to a medical friend.