of Latitudes for Local Attraction. 333 



This, however, may be explained, irrespective of the fact that 

 what has been effected is only experimental, by considering 

 that, notwithstanding all the labour and expense bestowed 

 thereupon, the levelling operations in Great Britain have not 

 yet progressed so far as to furnish such satisfactory data re- 

 garding the surface inequalities for all points as are available 

 for those stations at which this work has actually been done. 

 In Eussia, on the other hand, as we know, the greater part of 

 the triangulation is distinct from the arc. Any survey station 

 which has been precisely determined astronomically would 

 here serve the purpose for geological inquiry as well as an 

 arc-station. The next question would then be, at which of 

 these stations shall the inquiry be undertaken? In our 

 opinion this question should be answered in this sense — that 

 such points deserve to be worked as have an especially geo- 

 logical interest ; points where already a marked local attraction 

 is indicated, or where local peculiarities, such as mountain 

 masses or depressions, promise evidence on particular doubts. 

 In connection with this last category, Dollen has already 

 alluded to the Caucasian survey. And, indeed, we may hope 

 that by the prosecution under General Chodsko's direction of 

 that triangulation, which, cutting the Caucasus nearly in the 

 direction of the meridian, is intended to connect the Trans- 

 caucasian survey with that which has been executed in the 

 southern part of European Russia, very valuable material 

 will in the course of a few years be available for the confir- 

 mation or reversal of Airy's hypothetical explanation of the 

 nearly inappreciable influence of the Himalayas upon the 

 plumb-line. 



Under the first category of points, namely such as are 

 already indicated by remarkable local attraction, a prominent 

 place must certainly be assigned in Russia to Moscow. From a 

 large number of points, chiefly on the borders of the province 

 of Moscow, connected independently of each other with the 

 Moscow Observator}', the latitude of this last, gedoetically in- 

 ferred, is found to differ on an average 10" from the directly 

 observed value. In a district apparently so little irregular as 

 that which surrounds Moscow such a phenomenon is certainly 

 to be regarded as startling. The magnitude of the deviation 

 amounts to about four times the mean value of local attraction 

 for any unspecified place on the earth's surface, as presented 

 by the nearly coincident determinations, first, of Bessel, and 

 more recently, of Clarke, in their works on the figure of the 

 earth. Here, then, it behoves to make sure of the fact in the first 

 place by the most precise measurements ; then to trace the 

 course of the anomaly in the neighbourhood; and then perhaps, 



