sufficient to carry us down exactly the twenty steps; it is evident that the Will was set in motion to descend the imaginary twentieth step with as much force as it was at the first step. But the best illustration of unconscious voluntary action is perhaps afforded by the motion of the fingers in writing, where the warmest advocate of the theory of habit can hardly maintain that the action is entirely consensual; and the storage of the Will hypothesis is evidently inadequate to account for each separate motion of the fingers, which must require a distinct action of the Will, exercised perfectly unconsciously to ourselves. The lateral motion of the eye-balls, again, which takes place in reading, is one evidently entirely under the control of the Will, and is yet performed with the most perfect unconsciousness.

We appear to have dwelt rather on those points in which we differ from Mr. Murphy than on those in which we agree with him. There is, however, much in these two volumes that will interest every student of Biology and of Psychology, and not a little that must commend itself to the attention of every man of science. Whatever acceptance his views may meet with in the scientific world, it is impossible not to acknowledge the fairness and moderation with which he has brought them forward, and the ability with which he has supported them by logical argument and by a large array of facts.

JEFFREYS' BRITISH CONCHOLOGY.*

FROM the various reports which have from time to time appeared in these pages, of the dredging expeditions of the author of this work, as well as from the notice of the second volume of a portion of the work itself, which is to be found as far back as in our first volume, our readers will have become well acquainted with the active labours of Mr. Gwyn Jeffreys. The publication of the work has extended over seven years, and all we can attempt to do here is to give a brief outline of its contents.

The first volume deals with "land and fresh-water shells," the remaining four with "marine shells;" but from this it must not be inferred that the author's labours have been confined to the description of shells alone. The book is an excellent and complete treatise on the Natural History of British Mollusca, containing not only accurate descriptions of the various genera and species in their zoological order, but accounts of their British habitat, as well

*British Conchology; or, an Account of the Mollusca which now inhabit the British Isles and the Surrounding Seas.' In 5 volumes (commencing 1862 and ending 1869). Illustrated with coloured and plain plates. By John Gwyn Jeffreys, F.R.S., F.G.S., &c. Van Voorst.

as of their geographical distribution. In addition to these details, the work is rendered interesting by such anecdotes and considerations as are calculated to relieve the tedium of study, and we have here and there incidents concerning the different kinds of molluscs, which form an agreeable diversion from the consideration of their anatomy, the form and colour of their shells, and the divergences of species.

In speaking of Helix aspersa, the author tells us* "they make great havoc in kitchen gardens, and spoil the best wall-fruit. There is, however, some compensation for this mischief: a kind of broth is made from them, and used as a remedy for pulmonary complaints. This kind of snail is occasionally eaten by the French; but it is not held by them in the same estimation as the AppleSnail. Dr. Gray says that the glassmen at Newcastle, once a-year, have a snail-feast, and that they generally collect the snails themselves in the fields and hedges the Sunday before feast-day."

Nor are the author's considerations on the subject confined either to the scientific or the utilitarian, if feasting on snails can be thus designated. He sometimes soars into the regions of poetry; or, as he calls it, the aesthetical. The snail could never secure a footing on Mount Parnassus, he tells us, but "we may enter the realms of phantasy and we shall find it among those intruders which had to be chased from the cradle of the fairy-queen." Homer did not disdain to use the snail's shell as a helmet for belligerent frogs, in his "mock heroic poem.' "The most imposing appearance," the author tells us," which the animal has made in literature," is to be found in Goethe's "wild vision of the Walpurgis Night," when, on the top of the Harz mountains, " an adventurous and preternaturally sensitive snail," "detected the presence and unmasked the incognito of not less a person than Mephistopheles himself." And the author gives us the quotation, describing the occurrence, which leaves no doubt that the snail must have been very preternaturally sensitive, for it was able to smell out the identity of the Evil One with its tentacles!

However, we do not suppose the author had any intention to press the great German poet into the service of science, so we will let that pass.

The first volume of the work treats, as we have said, of land and fresh-water shells; the second, of the marine molluscs, comprising the Brachiopoda and part of the Conchifera. In the third, the Conchifera are concluded, and the Solenoconchia and part of the Gasteropoda treated. The fourth continues the description of the great group Gasteropoda, which is concluded in the fifth volume, where also an account will be found of the higher molluscs, the Pteropoda and Cephalopoda.

* Vol. i., p. 183.

Each volume is accompanied with a beautiful coloured plate as a frontispiece, and numerous well-executed lithographs. It suffices to say that the whole work is produced in Mr. Van Voorst's best style, and will form a valuable addition to his well-known treatises of reference on Natural History.

SCHRAUF'S HANDBOOK OF PRECIOUS STONES.

To any one who is not familiar with the elements of mineralogy, a cabinet of precious stones-however rich and rare-has no more educational value than a collection of shells can have to a person ignorant of the anatomy of the mollusca. Yet it is by no means needful to plunge into the depths of mineralogic lore in order to appreciate the scientific value of a gem. All that is necessary is a moderate acquaintance with the physical and chemical characters of the comparatively few minerals which rank as precious stones, and of those substances which are likely to be mistaken for genuine gems. Dr. Schrauf, of Vienna, has recently published a textbook,* which gives, within a moderate compass, all that mineralogical information which the collector ought to have at hand.

The early chapters of the work are devoted to a discussion of mineralogical physics-a subject which no one can handle better than the author of the elaborate Lehrbuch der physikalischen Mineralogie.

Popularly, yet accurately, he tells us all that we need know on the crystalline form of minerals, their hardness, density, thermal, electric, magnetic, and optical properties. Then follows a chapter on the forms in which precious stones are commonly cut by the jeweller. Each gem is then described separately, in order of value, commencing, of course, with the diamond.

In the chapter on Diamond, our author proposes a new formula for determining the value of this stone-a formula which is said to give results coinciding with the present market value of diamonds, and is, moreover, applicable to stones of high weight. Let a denote the current price of one carat; then the value of a diamond weighing m carats will be, according to Schrauf's formula,

m (m + 2) a.

To illustrate the application of this rule, we may calculate the value of the celebrated Sancy diamond, which was sold only a year or two ago, and to which so romantic a history is attached. This *Handbuch der Edelsteinkunde,' von Dr. Albrecht Schrauf. Wien, 1869. Pp. 252.

VOL. VII.

G

diamond is said to weigh about 53 carats, and being only rose-cut, one carat may be valued at 157. Then, according to our rule, the value of the diamond may be thus expressed in pounds:

53 (53+2) 15 = 26.5 × 55 × 15 = 21,862.5.

It must be admitted that this is a tolerably near approximation to the true value, when it is stated that the diamond was sold by Prince Demidoff to Sir Jamsetjee Jejeebhoy for 20,0007.

Perhaps the most useful part of this work is to be found in the concluding chapters, which explain the method of determining an unknown gem, the results of which are afterwards collected in a tabular form.

We shall be glad to see so excellent a work as this translated into English.

SENFT'S MINERALOGY AND LITHOLOGY.*

IF one branch of natural science, more than another, deserves to find a place in any improved scheme of scholastic education, that science, according to Dr. Senft, is undoubtedly Mineralogy. For, apart from its practical value to all whose daily occupation brings them into contact, directly or indirectly, with the products of the mineral kingdom-such as the miner, the builder, the agriculturist, and the manufacturing chemist-the study of mineralogy is so closely connected with that of many collateral sciences that a course of mineralogical lectures, properly delivered, might be made the means of imparting to a class much valuable information on the sciences of chemistry, physics, and geology, to say nothing of solid geometry. Hitherto this relation of mineralogy to other branches of science has been regarded as a great stumbling-block to the student, inasmuch as he must needs acquire a rather wide range of knowledge before he can successfully cope with the difficulties of mineralogy. These difficulties may, however, be removed, to a great extent, by an attractive style of instruction, adapted to the capacity of the pupil, but at the same time not superficial enough to nullify the efficiency of mineralogical study as a means of intellectual training. Five-and-twenty years' experience in teaching science to youths between fourteen and sixteen years of age, has led our author to mature a scheme of instruction which he regards as best adapted to meet the wants of those who may not wish to push their mineralogical studies beyond a very moderate acquaintance with the more important species. He devotes to this study only two hours weekly, but he extends the course over two years. The

*Lehrbuch der Mineralien und Felsartenkunde. Von Dr. Ferdinand Senft 8vo. Jena, 1869. Pp. 656.

first year's course is only preparatory, and chiefly chemical. The student first learns the properties of the elements, and thus becomes, to some extent, acquainted with the characters of such species as the diamond, graphite, sulphur, and the native metals. He then advances to the study of simple chemical combinations, and is thus made acquainted with the chief acids and metallic oxides. This chemical course occupies a summer session, and is followed, during the succeeding winter course, by the study of the physical properties of minerals, as demonstrated on certain species of simple composition. Our author's mode of teaching may be illustrated by an example of his lesson on Quartz. A piece of common quartz is exhibited to the class, pulverized, and treated successively with water and the ordinary acids, for the purpose of showing its insolubility in these reagents. A small quantity is then mixed with an alkaline carbonate, and slowly heated for a quarter of an hour in an iron capsule. The effervescence consequent on the expulsion of the carbonic gas points to the acid character of silica; while the formation of a vitreous silicate illustrates the chemical composition of glass. During these experiments, an apt teacher will, of course, entertain his class by a valuable lesson on the manufacture of glass, and by explaining the method pursued in the analysis of siliceous minerals. Having thus become familiar with the chemical characters of the species, a well-formed piece of rock-crystal is exhibited to illustrate its crystalline form. The sixsided prism and its two terminal pyramids furnish a text for much instruction on the crystallography of the hexagonal system, whilst models of the forms are made in clay before the class, or, still better, by the students themselves. Attention is then directed to the other physical properties of quartz: its hardness is shown by its resistance to the knife, and by striking sparks with steel; its specific gravity is taken; its phosphorescence exhibited; and electricity is developed by friction. In this way the student becomes interested in chemical and physical science; and if no other scientific study be introduced into a system of general education, much solid instruction can be imparted by a judicious study of our common minerals.

The second year's course comprehends work of a more strictly scientific character, and includes the principles of classification and a description of the more important mineralogical species.

To supply a work adapted for instruction of this practical kind, Dr. Senft has prepared a useful Text-book of Mineralogy and Lithology. The first part is devoted to the general principles of mineralogy; the second, to a description of the principal species; and the third, to the study of rocks or aggregates of minerals. In the notice of species those only are described which have acquired importance by their wide distribution, by their applications in the