326 MM. Struve and Dollen on the Correction 



us that every objection would lose its force in presence of 

 such a fact ; nay, more, that thereby alone can a sure 

 position be won, from which to form our conceptions of the 

 origin and formation of the earth's crust, in place of the 

 very vague suppositions and conjectures with which we have 

 hitherto been obliged to be satisfied. Against this something 

 can indeed be advanced ; nevertheless we do not hesitate in the 

 least degree to acknowledge the great importance that would 

 attach to such a fact, were it well established. We think, 

 however, that we are for that xery reason doubly bound to 

 allow no lack of proper caution in establishing it ; first 

 noting carefully in each case all the connected circumstances, 

 and afterwards avoiding a general conclusion too hastily 

 drawn from particular cases. For such a conclusion to be 

 justified, it is not only necessary that it rest on a very con- 

 siderable number of separate carefully verified experiments, 

 but indispensable that these experiments have been made at 

 points as widely distributed as possible over the whole 

 surface. Yet when, with such restriction, we come to 

 examine the sum-total of fact at present at our disposal 

 upon this subject, the existing information proves to be 

 insignificant, compared with what is required : indeed, no 

 such scale is needed to show its utter inadequacy. But we 

 must restrain the desire to give an account, in any de- 

 gree correct, of the present state of facts in this important 

 matter : it would be impossible without minute examination, 

 the result of which would show most plainly that even the 

 materials separately, apart from their scarcity, are for the 

 most part far from sufficiently well-founded for any further 

 conclusion to be safely drawn from them. Thus for example, 

 for the cases from which, according to all likelihood, the most 

 decisive indications would be to be looked for, namely the 

 attraction of great chains of mountains, we have to depend 

 almost exclusively on the results of the second Indian arc, the 

 most northern stations of which are near enough to the 

 Himalaya mountains for a very important deflection of the 

 plumb-line to be expected. What is to be taught on this 

 point by the Alps and the Pyrenees has not yet been ex- 

 amined sufficiently for us to be able to say more than that great 

 deflections undoubtedly exist there. The same is true of 

 the mountains at the Cape of Good Hope. We may also 

 expect very valuable additions of information in future years 

 from the Caucasus ; but at present it is in the case of the 

 Himalayas alone that anything determinate has been ascer- 

 tained. Yet even here our present knowledge goes but a 

 little way towards giving any really clear idea of the true 



