O. N. Rood on Markings of Pleurosigma Angulatum. 335 
deflections of the magnetic needle here recorded, were caused by 
the electric currents which prevail during the presence of auro- 
ras; while others occurred when no aurora was noticed. During 
than when there is no aurora; but they all seem to follow the 
1837. Aug. 81. 10' y.m. Christiania. Slight aurora. i 
1837, Nov. 12. 644, England. Bright aurora with streamers reaching to the zenith. 
. ‘ n. 
Nov. 14, England. Broad patches and streamers of a fiery red color. 
Noy. 14. 114-12}, Christiania. Aurora of an intense crimson color. 
i urora. 
1838. Nov. 24. 10%, Christiania. A flaming auroral arch about 10° altitude. 
1839. Feb, 21, 61", Christiania. Aurora radiating towards the zenith, 
-9h, St. ra. 
: ‘0 
1840. Aug. 28. 104, Christiania. Slight se 
1841, Aug. 27, 912%, Christiania, Slight aurora, 
During the aurora of Sept. 2, 1859, the disturbance of the 
magnetic needle was very great at Toronto, Greenwich, Brussels, 
aris, Rome, Christiania, St. Petersburg, Catherinenburg, Nert- 
arnaul, but the observations are not reported wit 
nsk, an 
sufficient frequency to enable us to trace satisfactorily the pro- 
te within an hour of the same instant; it being impossible to 
etermine the coincidence more closely, for the observations at 
these three places are only given at intervals of one hour. 
New Haven, September, 1861. 
—_— 
Arr. XXXVIL.—On the evidence furnished by Photography as to 
the nature of the markings on the Pleurosigma Angulatum; by 
Prof. O. N. Roop, of Troy, New York. 
One part intaining i hexagonal, while their antagonists 
Pe oe Bee ate has been called upon to aid 
in a settlement, and photographs of this shell were obtained by 
Mr. Whenam, which distinctly exhibited the hexagonal structure. 
