THE FORCES OF N ATURE.* IT is by no means
easy to assign an exact position and value to the popular volumes on science lately given to the world by Figuier,
Flammarion, Simonin, Hartwig, and two or three other foreign authors. It may, on the one hand, be justly objected to such works, that their various parts are of unequal merit ; that they often exhibit a tendency to exaggeration or romance ; and that they are generally at once too superficial and too incomplete to be of use to the student of natural science and natural history, and too learned to be wholly acceptable in the drawing-room and the boudoir. Yet, on the other hand, we willingly allow that a volume like that before us on the Forces of Nature does offer, to unscientific but intelligent people, some glimpses of the hidden marvels and splendours of Nature, and may frequently excite, in apt and studious minds, a powerful desire for further and more profound knowledge.
The work before us is, on the whole, a satisfactory performance. Its aim is to be popular, and it achieves success by an easy style of writing, and by a selection of varied and telling illustrations. Certainly sometimes the illustrative diagrams and woodcuts are in advance of the text, which does not always offer complete -explanations of the apparatus and constructions which are figured. This is not to be wondered at, when we remember that many of these diagrams originally illustrated special memoirs of exhaustive and abstruse character. But as many of the woodcuts and chromolithographs represent striking phenomena by means of designs beautiful as to form or colour, the eye is appealed to and pleased, even if the mind be not wholly satisfied. Our readers may perhaps best appreciate M. Guillemin's sumptuous volume, if we endeavour to give them some idea of its adornments rather than of its explanations.
There are eleven coloured plates in this volume, the frontispiece showing the iris colours of a soap bubble, and the last plate those of a double rainbow. This last drawing is not good, the hues and proportions of the several chief elements of the rainbow being incorrect. The red and violet ends of this form of the solar spec- trum seem printed with the same pigment ; the yellow band is too prominent by far ; the blue is barely represented, while the green is irregular. Nor are the artistic constituents of the figure more commendable than the scientific, for the landscape introduced into this plate merely serves, through the feebleness of its design and execution, to intensify the general unsatisfactoriness of the illustration.
The nine chapters which constitute the first division of the work are devoted to the phenomena of gravity, weight, and specific gravity, including the methods of ascertaining the densities of solids, liquids, and gases. The illustrations here are generally good, though they occasionally show signs of wear, and in some cases do not represent the best forms of apparatus, nor those used in England. Into the description of the chemical balance (p. 56) several small errors have crept, besides those referred to in the list of errata. Five kilograms do not represent 13.39 lbs. avoirdu- pois ; while a good balance by Oertliug will indicate distinctly -one-tenth of a milligram, when each pan is loaded with 50 grams, not with two grams only.
Book II. contains ten chapters on Sound. As recent methods of investigating musical tones and timbres have introduced new methods of graphically illustrating the phenomena of sound, the diagrams which represent the ocular demonstrations of sonorous vibrations are of great interest and value, So, too, the anatomical drawings of the internal and the external apparatus of hearing in man serve to complete suitably the account of this subject. The beautiful figures obtained by means of tuning forks and vibrating strings are well shown in figs. 115, 116, 120, and 137, while some curious phenomena produced with gas-jets by means of sounds are described on pp. 199, et seq.
Of all subjects here discussed, that of Light, to which the eigh-
• The Forces of Nature. By Amddee Gaillemin. Translated by Mrs. N. Lockyer, London: Macmillan. 1872.
teen chapters of Book IV. are devoted, admits of the most ample and attractive illustration. Accordingly we find that most of the coloured plates in M. Guillemin's volume represent such phenomena as the spectra of various sources of light, monochromatic and poly- chromatic diffraction fringes, and Chevreul's chromatic circles and scales. So far as the execution of these plates is concerned, nothing but commendation can be awarded, and the details are generally accurate. But it is a pity that a simple illustration of the true theory of complementary colours, as developed by Helm- holtz and Maxwell, should not have replaced the erroneous chromatic circle of Chevreul. This is the more to be regretted, since nearly all works on the theory and practice of colour and decoration still ignore the recent advances of science in this direction, which are, however, partially noticed in the text of the work now under review. It is difficult to persuade artists that green and red are not complementary colours, but that bluish- green and red are ; that yellow and blue lights mingled form white light seems an enigma, while the statement that yellow may itself be produced by the combination of red and green rays seems at first contrary to experience. But it is now ascertained that the older views as to the relations of some of the primary colours were not only complicated, but rendered erroneous by the methods of observation adopted. Satisfactory conclusions can be reached only by the employment of rays of coloured light, not by the use of pigments.
The subject of solar and stellar light and the means of analysing it offered to us by the spectroscope are fairly discussed, while some of the most interesting revelations which have been obtained concerning the chemistry of the sun and stars are described tersely and intelligibly.. Some of the beat woodcuts in. this section of the volume are those relating to double refraction ; at the same time, we may bestow a passing expression of praise upon the very pretty landscape (fig. 164) introduced to illustrate the reflection of light. Some account of the organ of vision appro- priately concludes this section of the Forces of Nature.
The remainder of the volume gives illustrations of some of the chief phenomena, experiments, and apparatus relating to heat, magnetism, and electricity. Afinal chapter refers to meteorology. Plate vii., which represents a Polar aurora, like a fringed and luminous curtain, crimson and yellow-green, hung against the indigo of a northern sky, displays a far more startling and beautiful appearance than that of the ordinary aurora of our latitudes. The phosphorescent and fluorescent effects obtained by means of electric discharges through Geissler's vacuum-tubes are rendered with truth and delicacy by the figures of plate x. A woodcut (fig. 450) giving nearly one hundred snow- crystals, is worthy of careful study ; it, however, is not original, but, with the majority of the illustrations in M. Guillernin!s hook, has been used previously. Yet we cannot but praise the variety of the figures in these pages, and the judgment shown in the selection of those which were not expressly designed for the work. A few improve- ments may be usefully introduced into the text of a second issue, but, on the whole, the work of the translator and of the editor has been well done.
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