84 ANNUAL OF SCIENTIFIC DISCOVERY. 



Schweizer, Director of the Imperial Observatory of that city, have 

 established the existence of a local deviation to the extraordinary 

 amount of nineteen seconds, within a very short distance of that me- 

 tropolis. At Moscow, the plumb-line is found to deviate eight seconds 

 from the spheroidical perpendicular toward the north. At twenty 

 Russian versts (thirteen English miles) to the northward of Moscow, 

 this deviation ceases. It does so, also, at twelve versts (eight miles) to 

 the south of the city ; but on going farther south, it recommences in a 

 contrary direction, and at twenty-five versts to the south of Moscow is 

 converted into a southern deviation of eleven seconds. Proceeding from 

 Moscow in either an easterly or westerly direction, similar phenomena 

 are observed. As there is nothing deserving the name of a mountain 

 in the neighborhood of Moscow, it follows, as a necessary consequence, 

 from these facts, either, 1st. That there exist beneath Moscow enor- 

 mous cavities, occupied by air, or perhaps by water. 2d. That strata 

 of some substance of very weak specific gravity exist beneath that 

 city. Or, 3d, that there extends over the whole of the country sur- 

 rounding it a generally loose, unconsolidated mass of geological mate- 

 rial to a depth hopelessly beyond what human labor can ever expect to 

 penetrate. The interest of the observation does not terminate with 

 the particular case of Moscow, but seems to indicate that henceforth 

 in all instrumental determinations depending on the level or the 

 plumb line, attention must be given to the lithological character of 

 the place of observation. Here, again, is a point of contact between 

 the two antithetical sciences of astronomy and geology. 



DEFLECTION OF THE PLUMMET CAUSED BY THE SUN'S AND 



MOON'S ATTRACTION. 



Mr. Edward Sang, in a paper read to the Royal Society of Edin- 

 burgh, shows that the attraction of the sun causes a deflection of the 

 plummet, having its maximum about the 240th part of a second, and 

 proportional to twice the size of the sun's zenith distance ; the deflec- 

 tion is at its maximum when the sun is 45 above or below the horizon, 

 and occurs in the vertical plane passing through the attracting body. 

 The deflection due to the moon has its maximum about the 60th part 

 of a second, and follows the same law ; it is toward or from the attract- 

 ing body according as the zenkh distance is less or more than 90. 

 Upon the cross-level of a transit instrument, the joint effect is to cause 

 a semi-diurnal oscillation, small at the quarters and rising to the 24th 

 part of a second at new and full moon ; while the influence upon me- 

 ridian observations is sufficient to cause a disagreement between the 

 greatest inclination of the moon's orbit, as observed at St. Petersburg 

 and Madras, amounting to the fiftieth of a second. 



The general conclusion drawn was, that we cannot determine the 

 positions of the heavenly bodies true to the one hundredth part of a 

 second, without having made allowance for this source of disturbance. 



MEAN DENSITY OF THE EARTH. 



In a memoir on this subject, by M. Faye, read at a recent meeting 

 of the French Academy, the following valuations, from pendulum ex- 

 periments, are given : 4.39 by Caiiini and Plana, at Mount Cenis ; 

 4,71 by Maskelyne, Ilutton, and Playfair, at Schehallien, in Scotland; 



