Dec. 9, 1S80 



NA TURE 



almost exclusively. The article is divided into the two 

 sections of plane and sohd geometry. At the commence- 

 ment the student is recommended by the weight of Prof. 

 Cayley's adxice to trace a number of cur\-es, and he 

 draws a few simple ones, so drawing attention to a point 

 upon which Mr. Frost, in his " Curve-Tracing," strongly 

 insists. Prof. Clifford, too, we believe, had it in his mind 

 to publish an account of some methods which " are ex- 

 ceedingly simple and easy of application ; they partake 

 more of the nature of a manual craft than of a purely 

 intellectual occupation, and may so be used as a rest from 

 severer studies ; and, as we can only imagine things of 

 which we have seen the like by .appealing directly to the 

 senses, they extend those powers of concrete realisation 

 which the growing complication of modern analysis 

 renders daily more desirable." The methods he alluded 

 to are " Projection, a process by which no alteration is 

 made in the order, the class, nor in any other purely 

 descriptive property of a curve;" then "those modifi- 

 cations of form which leave the . order of a curve 

 unaltered ; " then " those changes which exercise no 

 effect upon the class." In the last two cases he proposed 

 to use a process which he used to call "ihe composilioii 

 of curves, by which a curve of any order or class may 

 be built up out of the simplest elements." We fear that 

 we have lost this proposed sketch, with the many other 

 sketches he had outlined and lived not long enough to 

 endue with a vitality he could so well have given them. 

 After the illustrations referred to Prof. Cayley discusses 

 shortly the metrical theory, and obtains the several 

 familiar equations both in plane and solid geometry. In 

 short paragraphs polar, trilinear, point, and line co-ordi- 

 nates are described, but not applied. We have noted 

 scarcely any misprints in the first article, but in the second 

 there are several, all of which are easily detected. The 

 figures are very well done. 



We would draw attention to the article on Geodesy by 

 Col. Clarke, which we have read with much pleasure. 

 It is well illustrated, and the eighteen columns treat of 

 the following matters : — Horizontal angles, astronomical 

 observations, calculation of triangulation, irregularities 

 of the earth's surface, altitudes, longitude. These are as 

 fully discussed as need be in a sketch of the subject, and 

 we shall expect that Col. Clarke's more extended work on 

 Geodesy, referred to in Nature, vol. xxi. p. 423, will 

 take its place as a standard work for some time to come. 



Geology occupies at the present day so important 

 a position in the circle of the sciences that it de- 

 serves to be treated, in any modern cyclopasdia, with 

 no niggard hand. A slender essay, confined to a survey 

 of the broad features of geology, would have been sadly 

 disappointing in such a work as the " Encyclopaedia 

 Britannica." It is therefore satisfactory to observe that 

 Prof. Geikie, to whom the editor entrusted this article, 

 has put a liberal interpretation upon his trust. He has 

 treated his subject with a fulness worthy of a great and 

 growing science, and worthy too of the noble plan 

 upon which the Encyclopaedia has been projected. The 

 masterly article which he has contributed to the new 

 edition ■ stretches over more than 320 columns, and is 

 thus longer than most of the kindred articles, such as 

 those on "Astronomy" and "Chemistry." Possibly it 



might have borne, here and there, a little condensation, 

 but on the whole it is admirably fitted for its place. It 

 stands forth as a solid and comprehensive monograph 

 which, if reprinted from the Cyclopaedia, w'Ould form 

 one of the most substantial treatises in our geological litera- 

 ture. But the article is not only substantial, it is, like all 

 Prof. Geikie' s writings, eminently readable. The cardina 

 virtues of an encyclopaedist are accuracy and conciseness 

 of expression, and he usually finds but little scope for the 

 play of liter.iry graces. Prof. Geikie, however, is far too 

 polished an author to write upon any subject in an un- 

 attractive style; and the present article is sufficient to 

 prove— were proof needed — that his graceful pen does 

 not fail him, even when discoursing on the knottiest point in 

 geology. The comprehensive nature of this article, and the 

 originality with which the subject is treated, may be best 

 shown by explaining the seven-fold division adopted by 

 the author. First he deals with the Cosiiiical Aspects oj 

 Geology, and not only discusses the shape and the motions 

 of the earth, but stretches his survey to the probable 

 history of the solar system. Then he inquires into the 

 nature of the materials of the earth's substance— an 

 inquiry which falls under the head of Geognosy. In the 

 early part of the article the author may seem to trench a 

 little upon subjects which are treated in other articles, 

 but this is almost inevitable in any cyclopaedia. It is not 

 to be expected that the several essays shall just touch 

 each other without overlap, like the pieces of a neatly-jointed 

 mosaic. The geognostic division of the article is followed 

 by a section on Dynamical Geology, and this in turn by one 

 on Siruetnnil Geology, or the architecture of the earth. 

 Under the head of Paheontological Geology Prof. Geikie 

 sketches the history of life as revealed by the fossiliferous 

 deposits, while in the following section onStra/igrapliieal 

 Geology he traces the chronological succession of events 

 in the history of the stratified rocks. Finally a chapter 

 is devoted to Physiographical Geology, or a discussion 

 of the origin of the physical features of the earth's 

 surface. 



To see for the first time a great actor play the part of a 

 familiar character is a treat ; but the pleasure is seldoni 

 quite free from a mixture of disappointment. His reading 

 of the part is usually not our pet and peculiar one, and 

 we are, as it were, buUied into contentment by the great 

 power of the performer. We felt something akin to it 

 when we read the article " Heat " by Sir William 

 Thomson, though the feeling was of course unreason- 

 able. It often happens when for the second time we see a 

 great actor play a great part we yield ourselves to his charm 

 without a trace of intellectual reserve ; so it will most 

 likely be when next we read the article " Heat." At all 

 events, the readers of Nature may be assured that there 

 is little in this article that they can justly find fault with, 

 whatever they may miss to find that they expected. 

 Could it be otherwise, when the author is the pupil of 

 Regnault, the colleague of Joule, one of the patriarchs of 

 the modern science of thermodynamics, the greatest 

 living authority on the theory of heat in Britain ? We 

 shall therefore most modestly discharge our function by 

 pointing out to our readers what they will find in Sir 

 William Thomson's article ; and by slightly indicating some 

 points on which, to our regret, he has withheld his opinion. 



