THE AERIAL WORLD.*
Da. HARTWIG has compiled several large and interesting volumes on popular science, somewhat sensational in character, but on the whole calculated to serve a useful purpose. Yet we find it difficult to commend his books. We hesitate simply because we question how far any one is entitled to put his name, except professedly as a mere compiler, to volumes con- sisting in a large degree of borrowed matter, if judged accord- ing to mere quantity, and almost entirely composed of such matter if judged by their scientific value. To speak plainly, Dr. Hartwig appears to have no opinion of his own upon the subjects whereof his volumes treat. He gathers together interesting passages from the writings of Tyndall, Glaisher, and others, amusing narratives from various books, and more or less apt quotations from the poets. He presents these in company with striking pictures, not always strictly scientific in character. And as a thread to keep these beads, of greater or less intrinsic value, together, he supplies a series of no very valuable reflections. And yet this book, like the others to which his name is attached, is one to be recommended, if its author is not to be very warmly commended. It serves the purpose described in the preface, giving " a general view of the phenomena of the atmosphere, pointing out the manifold relations between the aerial ocean and man, and describing the life of which it is the ever-busy scene." But it has not been " by writing this book " that this purpose hai been achieved." Dr. Hartwig's " time and labour " may not " be con- sidered as ill-spent," since certainly, " after a perusal of its con- tents, the reader," previously unacquainted with the wonders of the aerial world, will " find his interest in the great pages of nature more keenly awakened, and be led to deeper thought and further inquiry ;" but we should not, for our own part, consider this result due to the time and labour "bestowed upon the com- position" of the work, unless by composition we are to under- stand compilation.
In treating such a volume as the present as an original treatise on popular science, there are three points to which our attention would naturally be directed,—literary style, lucidity of exposi- tion, and insight into the physical relations dealt with. In all three points, the volume is characterised by very manifest defects. Dr. Hartwig appears to labour under the mistake of supposing that grandiloquence is a necessary quality in the description of the operations of nature ; and the fine writing in which he indulges is placed precisely where fine writing is least effective, at the
* The Aerial World: a Popular Account of the Phenomena and Life of the Atmosphere.
By G. Hartwig. London: Longman and Co. 1874.
beginning of the several chapters. When a writer, after describing the wonders of some field of nature, allows himself to be carried away for a short time by the feelings naturally excited by their contemplation, he takes the reader along with him, and may even without offence speak with a warmth and enthusiasm which, coldly judged, might appear excessive. But to open chapter after chapter with an attempt at fine writing is altogether in bad taste. Occasionally our author's desire to write finely leads to bathos, as where he tells us that " a storm viewed from within its caul- dron is rather a terrible thing, though the very fact of being caught up in the midst of one of Nature's laboratory-furnaces makes one feel resigned." Elsewhere, Dr. Hartwig's writing reminds one of the style used in advertisements, as where he
writes of the sea air that "in purity and invigorating quali- ties it is rivalled by mountain air, which is fortunately be-
coming more and more appreciated, as is fully proved by the constantly increasing number of sanatoria and pensions in the Swiss Alps, where the valetudinarian inhales health with every breath, and at the same time enjoys the sublimest scenery."
Dr. Hartwig fails in explanation, as might be expected, through his fondness for fine writing. But he also appears to have no clear idea of the requirements of the general reader. Take, for instance, the chapter on " Dew." After two pages of enthusiasm, including a paragraph on " fair believers in the virtues of dew as a cosmetic," he proceeds :—" As late as the beginning of the present century, natural philosophers were still disputing whether dew was formed from vapours ascending from the earth during the Right-time, or from the descent of such as had been already raised through the day, both parties endeavouring to justify their opinions by fanciful theories. At length, Dr. Wells, a London physician, struck out the true path of careful observation, and fully proved that dew is occasioned by the chilling which bodies near the surface of the earth experience in consequence of nocturnal radiation. Their temperature having then sunk several degrees below that of the circumambient air, it frequently hap- pens that this temperature is below that at which the atmosphere is saturated. The layer of air which is immediately in contact with that of the chilled bodies, and which virtually has the same tem- perature, then deposits a portion of the vapour which it contains ; in the same manner as a bottle of cold water, when brought into a warm room, becomes covered with moisture in consequence of
the condensation of aqueous vapour upon its surface." There is no explanation here, properly so termed. The last few words are typical of the whole passage. They amount to this statement,—
that a bottle of cold water becomes covered with moisture because water forms upon it. In the same manner, the illustration by means of the bottle of cold water in no way explains the formation of dew ; it amounts merely to the assertion that when objects become colder than the surrounding air, moisture collects on them,
in the same way that moisture collects on a bottle colder than the
surrounding air, and it would be quite as much to the purpose to say that the deposition of moisture on a cold bottle brought into a warm room is illustrated by the formation of dew on cold bodies at night. What the reader requires to have explained to him is the fact that the warmer air is, the greater is the quantity of water it is capable of retaining in the form of invisible vapour ; whence it follows that if air is saturated at a certain temperature, any circumstance which lowers its temperature compels the air to part with a portion of the aqueous vapour, which condenses in the form of minute drops of water.
As respects the interpretation of phenomena, Dr. Hartwig is content to follow the same authorities from whom he quotes largely in descriptive matter, and he adopts at times a tone implying that he would consider it in bad taste to express an opinion of his own. We would submit that an author who feels so strongly that his opinion on scientific matters is not wanted, might not unreasonably doubt whether he ought to make a hook on such matters.
It will be seen that the work before us possesses none of the characteristics which we expect to find in an original treatise.
Regarded, however, as a compilation, it may be described in more favourable terms. If there are many passages which have no scientific value, there are few which are not interesting. The outside of the volume indicates in a significant manner the aim of the compiler. It presents a picture of a balloon in flames, with two men falling from the car ; and we may safely say that readers likely to be attracted by the promise which such a picture suggests will not be disappointed by the contents of Dr. Hartwig's latest compilation.
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