NATURE 



605 



THURSDAY, APRIL 29, iS 



GEODESY 



Geodesy. By Col. A. R. Clarke, C.B., R.E., F.R.S., &c. 



(Oxford : Clarendon Press, 1880.) 



IT is well that there are men brave with the pen as 

 there are others brave with the surgeon's knife or the 

 soldier's bayonet — to whose actions the word temerity can 

 only be applied in the full consciousness that the moving 

 force which impels tbem is neither vainglory nor ignor- 

 ance, but a strong sense that providence or fate has 

 placed them in a position where, and when, they, and 

 they only, must obey that call which they feel to be the 

 duty of the moment. 



It is not often that this call is so clear to the literary 

 and scientific ear as it has come to be in the province 

 marked broadly on the map of knowledge as Geodesy. 

 And certainly there are few men in England to whose 

 ear we may believe that such a call could have been more 

 directly addressed than to that of the author of this work. 

 It is well, wc say, that he has bravely attended to it. 



The work to which Col. Clarke has set his hand and 

 seal was one to be dreamt of rather than executed, and 

 we doubt if the worst we could say of the finished deed 

 would not find something more than an echo in the mind 

 of so careful an author. For in truth the task was one of 

 very serious difficulty ; and it is in no depreciatory spirit, 

 but quite the reverse, that we have to recognise, by their 

 absence, the chapters — we might almost say the volumes 

 — on various branches of the great subject which we 

 cannot help looking for in a work bearing so broad a title 

 as ''• Geodesy." 



It would be difficult, if not impossible, to treat such a 

 subject as geodesy in a manner calculated to enlighten 

 the present generation as to the present position of the 

 questions which it has raised, without constant reference 

 to the stages through which it has passed. Cousin 

 germane to astronomy, it may claim to be treated with 

 some measure of the respect which has given rise to so 

 many histories of that science ; but geodesy can as yet 

 boast no historian. It is a strange fact, and the reason 

 of it is by no means so obvious as the fact is to be 

 regretted. One immediate consequence is that a writer 

 eminently competent to write a treatise on theoretical and 

 practical geodesy is debarred from doing so without the 

 arriire pensi'e of a neglected history — in which depart- 

 ment he labours under an obvious pressure of other 

 demands. Thus the first chapter of the work before us 

 reminds one of the explanations which are given to a 

 visitor to some manufactory, who comes out at the end 

 of a series of workshops with a general sense of having had 

 glimpses of interesting work, and a recollection of words 

 having a scarcely understood connection with the pro- 

 cesses witnessed ; but quite certain, if he paid the same 

 visit a hundred times in the same hurried manner, that 

 he could not understand the manufacture well. There 

 are many points in this first chapter which are either 

 historically inaccurate or so Collocated as, while capable 

 perhaps of correct interpretation, to suggest to a mind 

 previously unread more or less erroneous conceptions. 

 It is needless to give instances ; for besides that they 

 Vol. xxi.— No. 548 



would but concentrate a needless criticism on points of 

 detail, it is evident that a full account of geodetical opera- 

 tions during two centuries and a half cannot be given in 

 a chapter of thirty-six octavo pages, a very considerable 

 portion of which is taken up with tables, diagrams, 

 mathematical explanations, and numerical examples. 



Remarking here, as elsewhere throughout the volume, 

 the author's neglect of the opportunities which are 

 afforded, in the course of a relation of facts, to explain 

 causes of failure, to comment on erroneous and vitiating 

 opinions, as well as to commend those which have borne 

 the test of later experience ; in a word, to take upon him 

 the burden of judging wherein lay the foundations of what 

 may now be recognised as sound principle — remarking 

 this abstinence, we are the more pleased to notice and to 

 give some slight additional currency to an exception, 

 which finds expression in at least three places in different 

 parts of the work. It is a condemnation of systems of 

 observation which do not aim at " the ' bugbear ' constant 

 error, which is, or should be, the first and last anxiety of 

 every observer." It will be long before a rule, which has 

 all the appearance of courting error rather than truth, 

 will be so generally recognised as to need no "bushing." 

 Meanwhile let it stand forth : — 



Presume the existence of a constant effect as the 

 natural concomitant of constant conditions, and if such 

 effect is not itself the object of inquiry, destroy it by 

 opposing conditions, or baffle it by varying them. 



At the same time let it be noted that in very many 

 kinds of physical observation, that which is sought 

 depends directly on a difference of results, and where this 

 is the case constant errors require to be regarded in a 

 very different light. Geodesy is full of such cases, and 

 one of the most important is to be found in the use of the 

 differential pendulum, where maintenance of condition is 

 the sine qua non of exact result. 



The work before us consists of fourteen chapters, each 

 of which is devoted to one particular branch of the 

 subject ; and these, on the whole, form a tolerably con- 

 nected chain of narrative, argument, theory, explanation 

 and illustration, calculation, and discussion of result. 

 Considered as a work on geodesy, it is noteworthy that the 

 last chapter but one (Chapter XIII.) discusses the Figure 

 of the Earth, while the last is devoted, self-contained, to 

 the theory, practice, and results of observation with pendu- 

 lums. The inference to be drawn from this division is 

 that whatever is to be gathered regarding the earth's form 

 from pendulums is outside of the region of geodesy. So 

 far is this from being our own view, that we would 

 rather have seen this relegated chapter occupying its 

 legitimate historical place as at least the second if not 

 the first in the book. As such it shall be dealt with here. 



The mathematics of this part of the subject are very 

 brief and to the point. None of the numerous difficul- 

 ties are even mentioned here which have at one time 

 or another cropped up, and upon which pages innumer- 

 able have been written, printed, and published — to won- 

 derfully little purpose, so far as the practical accuracy 

 of pendulum observations is concerned, but not, perhaps, 

 altogether without influence on collateral physical in- 

 quiries. The history of pendulum observations is also 

 very briefly dismissed, with less inaccuracy than com- 

 monly falls to its lot. The " invariable " pendulum is of 



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