Miscellanies. 213 



each division of which corresponds to 43".22 of arc. The visual angle 

 under which each division is seen is so considerable, that the divisions 

 can readily be subdivided into tenths by estimation. The time of vibra- 

 tion of the magnet is 17".78. The apparatus containing the magnet, as 

 well as the reading telescope, are supported on stone pillars resting on 

 solid masonry and insulated from the floor. 



The observations having been undertaken by Prof Hoyd without as- 

 sistance, it was found impracticable to observe at intervals shorter than 

 the time of vibration of the magnet bar, of which each successive elon- 

 gation was accordingly noted. The time shown by the chronometer was 

 usually noted every tenth or twelfth vibration ; and thus the time of the 

 intervening observations could be interpolated with much exactness. The 

 error of the chronometer was obtained on the nights of the 11th, 14th, 

 and 19th of November, by transit observations with the four-foot transit 

 of the Observatory. 



Of these observations, those made on Wednesday, Nov. 13, (8 — 9,) 

 P. M. Greenwich mean time, were the most favorable for the purpose 

 contemplated. The changes, though small, (from 5" to 50",) were 

 marked and rapid, the intervals of the successive maxima and minima 

 averaging thirty six seconds. The epoch of their occurrence seems to 

 be determinable to between four and five seconds. 



When the two sets of observations were reduced and laid down in 

 curves, it was found that they presented no similarity ; in other words, 

 that there was no correspondence whatever between the smaller changes of 

 the declination at Dublin and at Philadelphia. The determination of 

 differences of longitude, by means of the magnet, is therefore, impracti- 

 cable at such distances ; but the attempt has revealed the important fact, 

 that the irregular changes of declination, which have exhibited so marked 

 a correspondence at the most distant stations at which simultaneous ob- 

 servations have been heretofore made, do not correspond on the American 

 and European continents. Prof Lloyd observed that much light would, 

 ere long, be thrown upon this curious subject, by a comparison of the ob- 

 servations made at the Magnetical Observatory of Toronto, in Upper Can- 

 ada, with those of Europe. 



22. Fossil Foraminifera in the Green Sand of New Jersey. — Prof 

 J. W. Bailey, in a recent visit to the cretaceous formations of New Jersey, 

 has brought to light the interesting fact that a large portion of the calca- 

 reous rock defined by Prof H. D. Rogers as the third formation of the 

 upper secondary, is made up, at the localities where he examined it, of 

 great quantities of microscopic shells, belonging to the Foraminifera of 

 D'Orbigny, which order includes those multilocular shells which compose 

 a large part of the calcareous sands, dtc. of Grignon and other localities 

 in the tertiary deposits of Europe. Since the minute multilocular shells 



