438 Supposed Connection of Meteoric Phenomena, 



point had sunk from 47 \° to 9J°: there was no aurora ; but 

 " the comet, or zodiacal light, of Mr. Olmsted comes to our 

 aid." Now, on March 31. there was a strong wind from the 

 s.w. The temperature was 40°, the dew point 13° ; the upper 

 clouds came from s.w., the middle from w., the upper clouds 

 hidden. The lower current blew strong from s.w., but changed 

 to n., on April 2., between 7 and 8 o'clock. The dew point 

 rose to 56° until a.m. April 2. ; it fell p.m. ; and in the evening 

 there was no aurora in north-west, and at the same time a 

 faint aurora in the east. On April 3. the dew point fell 32°, 

 in 24 hours, with three currents. An aurora followed. On 

 April 4. there was an aurora under similar circumstances, the 

 dew point, on 6th a.m., being down to 15°. 



As these auroras were not seen near Wilmington, Delaware, 

 on any of these nights (nor on any night in March, April, 

 May, or June), the presumption is, that they were not three, 

 nor even two, miles high. Of fifteen aurorse seen at Wilming- 

 ton, from July 10. 1831, till Dec. 15. 1833, only two were 

 seen at Philadelphia. But there was in all these cases a sud- 

 den and unusually great change in the dew point, twelve falls 

 and three rises. Of the three aurorae corresponding to the 

 three rises, one (March 17. 1833) was seen as an arch in the 

 zenith at Philadelphia. 



The following dates mark periods of extraordinary depres- 

 sion of the dew point without an aurora at Philadelphia. [I 

 have put them into a tabular form for convenience.] Whether 

 an aurora occurred elsewhere to the north, is not yet known. 



