PETER1tANN AND MILNER'S PHYSICAL GEOGRAPHY. * THE difference between a great

original genius and the useful but inferior class of improvers, inventors, imitators, and what not, really lies in comprehension : it is the largeness, the wholeness, the one entire and perfect principle, that may contain more than the discoverer himself sees or knows, and leaves nothing to be done but to carry out Half the globe was laid open by Columbus, though Columbus himself scarcely touched the continent of America; while he was in search of Asia, and thought he was on the road to Paradise. When Watt made his discoveries in steam, the imme- diate application was of limited utility; but he had announced the law of that which has created the manufactures of the modern

• The Atlas of Physical Geography: constructed by Augustus Petermann, F.R.G.S., Honorary Member of the Geographical Society at Berlin, &c. &c. With Descriptive Letterpress, embracing a General View of the Physical Phenomena of the Globe : by the Reverend Thomas Milner, M.A., F.R.G.S., Author of the " Gal- lery of Nature," &c. Illustrated by one hundred and thirty Vignettes on Wood. Published by Orr and'Co.

world, and enabled man to defy the winds and the waves : the merchant who ceases to measure by distance and only talks of hours, and the artisan who pays his pence for an afternoon's trip on the Thames, are far more indebted to the depth and largeness of the principle that Watt developed, than to the persons who adapted it to some new purpose, or the numbers who have improved the adaptations. It is the same in other things—poetry, art, science. The ori- ginal discoverer may not see the full extent of his discoveries, or may not have time, opportunity, patience, or inclination, to carry them fully out. The mere improver attains all at once, and is super- seded by the next comer. When Humboldt perceived the principle of showing the summer heat and winter cold of places of the same average temperature but with widely different latitudes, and marked them distinctly by drawing lines along the map, the ex- tension was not difficult to the monthly temperature ; or to the application of the same plan to other phsenomena that can be ex- hibited to the eye,—as the direction of winds, the currents of the ocean, the fall of rain, &c. Everybody who looks looks a map can see that the continents of the Old World extend from East to West, and of the New from North to South; that the great moun- tain chains respectively run in the same direction ; and that these govern the course of rivers, and influence otherphysical phmnomena. But of the myriads upon myriads who have looked at maps since the true extent of the globe was known, few who saw these obvious features saw the principles lurking under them. It was not the same in extent, but it was in degree, with the various volcanic and geological facts. When once the principle is laid down in its comprehension, numbers can apply and improve it. It is the great discoverer who is the great man. Only let the law be stated so that it can be apprehended by the learned, (it has been said that not twelve men in Europe could understand the Prineipia ) and it is certain in time to be popularized by able though inferior minds ; or, the cue once given, it will be applied to use, if only by trading speculators. If Humboldt's connexion with Berghaus's Physical Atlas had been much less than it was, still the merit of first fully considering the world in its structure and physical phenomena must be as- cribed to him ; not forgetting the previous observations of Cook's companion Foster, or the subsequent views of Bitter. Since Hum- boldt first turned his thoughts in this direction, more than half a century has elapsed • for the popular application of principles re- quires an accumulation of fpots and means, and in this case of geo- graphy they must be slowly collected and methodized. Once ma- tured, " physical geography," like other novelties, seems likely to become a fashion. Berghaus has supplied the Continent; Mr. Johnston of Edinburgh has published two large and very elabo- rate Atlases, at the price, we believe, of ten guineas and two guineas and a half respectively; several minor publications of an introductory kind or for the use of schools have appeared • and now we have before us a popular medium between the two classes, at a guinea—the maps constructed by Petermann, who was for many years an assistant of Berghaus—the descriptive letterpress done by Mr. Milner, who is well known for various works con- nected with the nature of the world and the universe.

And of all the various books we have seen upon the subject, Petermann's and Milner's is the most cleverly popular. The maps are designed in a manner to tell upon the eye as well as to show the pha3nomena. The mode of marking the mountain ranges by black lines, the thickness of the line being indicative of the heights, is abandoned for the more picturelike method of shading; which certainly makes a prettier map, and at once says " This is a moun- tain." It strikes us that an effort has also been made to mark the varying phenomena with more accuracy, by more numerous gra- dations of shading ; which, as in the ram-map, may accomplish its purpose, but with the effect of blackness in the deeper parts. The text is interspersed with a great many rather striking wood- cuts ; consisting of landscapes, heads, animals, trees and natural phtenomena, sometimes connected with the text, sometimes only re- lating to the general subject, and attractive rather than informing. The principal subjects or pluenomena treated of in the letterpress, or illustrated in the maps, are-1. Geology : 2. Hydrography ; show- ing the course, temperature, &o., of the ocean currents : 3. Meteor- ology : 4. Botanical and Zoological Geography ; with Ethnogra- phy, or the divisions of the human race : 5. Special maps on the British Isles and Palestine. These maps are sixteen in number ; and upon all their various subjects Mr. Milner brings the facts together with judgment and presents them with skill. The different features are clearly displayed, and where they admit of tabular grouping and exhibition, with great impressiveness and use,—as in the rivers, &c. of the British Isles. The reader has the salient ints and the most remarkable pluenomena clearly .put

before , with the attractiveness that flows from practised ability ; but perhaps the expositions are deficient in wholeness. As an example of Mr. Milner's matter and mode of treatment, we will take a few extracts. This is an explanation of " blue water " and the other colours of the ocean.

" The waters of the globe exhibit various hues, which depend upon a va- riety of circumstances. The ocean absorbs all the prismatic colours except that of ultramarine, which is reflected in every direction. This is its true colour in general, when seen apart from atmospheric influence, modified by depth ; but every gleam of sunshine, passing clouds, winds, shoals, and sandbanks, affect its Huts. Particular parts of the ocean show peculiar co-

lours. The sea is white in the Gulf of Guinea; black amid the Maldive Islands. Variously purple, red, and rose-colourd waters occur in the higher parts of the Mediterranean, in the vermilion sea off California, the Red Sea, and in tracts along the coasts of Chili, Brazil, and Australia. Green water appears in the Persian Gulf, off the Arabian coast, and in connexion with the deepest blue in the Arctic Ocean. These appearances are permanent, and so distinct that ships have been seen partly in blue and partly in green water at the same time.

" These tints are occasioned by differently-coloured animalcules, which swarm in countless myriads in the tracts in question. The same species (Triehodesmium erythrceura) which colour the Red Sea, have been found in other similarly-tinted districts of the ocean. The green of the Arctic Seas is produced also by minute animals, which visit in spring the coast of Holland, and have been encountered in immense shoals migrating in the Atlantic. In the Antartic regions, Sir James Ross remarked repeatedly the change of co- lour of the sea from light oceanic blue to a dirty brown, caused by ferru- ginous animalculie.

" The phosphorescence of the ocean, a magnificent and imposing spectacle, when the waves scintillate with bright green sparks, or exhibit a long line of fire flashing in a thousand directions, is mainly caused by minute organic beings, which are phosphorescent while alive • a property retained by the gelatinous particles with which certain tracts of the deep are thickly

charged their dead and dismembered relics. At the same time, a disturbed electrical condition of the atmosphere may be most favourable to the phze- nomenon."

The following passage contains a neat account of the velocity of zigzag and sheet lightning, as well as of its colours.

"The lightning of the first two classes does not last for more than one= thousandth of a second ; but a less duration in passing than one-millionth part of a second is attributed to the light of electricity of high tension. In comparison with this velocity, the most rapid artificial motion that can be pro4uced appears repose. This has been exemplified by Professor Wheat- stone in a very beautiful experiment. "A wheel, made to revolve with such celerity as to render its spokes in- visible, is seen for an instant with all its spokes distinct, as if at rest, when illuminated by a flash of lightning, because the flash has come and gone be- fore the wheel has had time to make a perceptible advance.

"The colour of lightning is variously orange, white, and blue., verging to violet. Its hue appears to depend on the intensity of electricity, and height in the atmosphere.

The more electricity there is passing through the air in a given time, the whiter and more dazzling is the light.

" Violet and blue coloured lightnings are observed to be discharged from storm-clouds high in the atmosphere, where the air is rarefied ; and analo- gously, the electric spark made to pass through the receiver of an air-pump exhibits a blue or violet light in proportion as the vacuum is complete."

These are curious- facts on man and temperature ; not new, but neatly put. " Owing mainly to the flexibility of his constitution, although obtaining much artificial aid, man can subsist under the greatest climatic extremes.. The Esquimaux endure the cold between the parallels of 70 dog. and 80 deg. ; the African Negroes subsist under the burning sun of the Equator ; while Europeans, accustomed to an intermediate temperature, have borne the rigour of the highest accessible latitude, and the fiercest heat of the Torrid zone.

" The power of the human frame to resist cold, according to Sir John Ross, who experienced four successive Arctic winters, appears to vary re- markablia'sizeidifferent constitutions. His general_ conclusion is, that the ruddy, elastic, florid, or clear-complexioned man, endowed with what phy- sicians call the sanguine temperament, has a peculiar power of retaining heat ; while those having pale, flabby, and sallow countenances, whose tem- perament is said to be phlegmatic or melancholic, are proportionately defi- cient. The most ample clothing 'will not compensate for the deficiency, since it can only retain the internal heat ; and if this be wanting, one might as well attempt to 4 warm a piece of ice by means of a blanket. He places his chief reliance on abundance of food ; and it is well known that the Esquimaux take as much as ten and twelve pounds' weight of animal food in twenty-four hours, its effect being heightened by the fat and oleaginoui quality of their diet. The oxygen which is inhaled with atmospheric air combines chemically with the carbon of the food, and that chemical action is the cause of heat and vital force. Therefore a much larger supply of animal food,. which contains many more times more carbon than vegetables, is necessary. in a cold climate ; while, amid torrid heat, rice and fruit form an appropriate diet."