334 On the Correction of Latitudes for Local Attraction. 



by recourse to extended levelling combined with inquiry into 

 the subsurface conditions, to reach some conclusion as to the 

 extent to which the anomaly is represented by the configuration 

 of the actual surface-strata. Under instructions from head- 

 quarters, Prof. Schweizer, the director of the observatory at 

 Moscow, has for several years been occupied with the first 

 of these duties, and we may shortly expect a publication of 

 the desired results. So far as we are aware, these operations, 

 interesting as they are, do not progress, on account of insuffi- 

 cient means, with either the accuracy or the rapidity which 

 their importance would seem to demand. 



Another striking anomaly seemed a few years ago to be de- 

 tected on the shores of the Ladoga Sea, at the town of 

 JSTavoya-Ladoga, the longitude of which, deduced geodetically, 

 differed notably from the astronomically determined value. 

 The attention of the Pulkova Observatory was consequently 

 directed to this point particularly, by reason of its neighbour- 

 hood. The difference, however, has been found much less 

 by more recent determinations, which have shown that the 

 former result was to a great extent due, partly to errors of 

 observation, and partly to numerical errors in the deter- 

 mination of the longitude-difference. What still remains as 

 the apparent local attraction at jSTovaya-Ladoga is neverthe- 

 less in excess of the average, being as much as 0*7 second of 

 longitude, w r hich in lat. 60° corresponds to 5 seconds of a 

 great circle. It is not large enough, however, to demand a 

 special investigation in this quarter. 



Dollen has also brought clearly before us that reliable 

 grounds for a decision as to the relation between local attraction 

 and crust- conformation can only be acquired by levelling 

 when it is of great extent. This is especially the case in 

 Russia, where the irregularities are as a rule individually in- 

 significant ; the general elevation or depression of the land 

 being, on the other hand, in certain directions very considerable. 

 It follows that if we desire to make real progress in Eussia 

 in this direction, it becomes essential to determine the rise 

 and fall of the land over as wide an extent as possible, by 

 means of a system of connected levels. It is known to the 

 Academy that the prosecution of such a general scheme of 

 levels has been proposed by the Government to the chief Ob- 

 servatory, for other and more immediately practical reasons ; 

 and various preliminary inquiries have already been instituted 

 with a view to ways and means to carry it into effect. 

 Should this design, as we hope, be shortly put into execution, 

 geology will certainly gain thereby a large body of material. 



Before we bring to an end this our judgment upon the 



