Atmosphmc Origin of the Aurora, 6j*c. 157 



auroras would have been the precursor. As tending to eluci- 

 date this new and interesting field of inquiry, I will state the re- 

 sults of observations on thirty two auroras observed at Schenec- 

 tady, N. Y., between Oct. 5, 1830, and Nov. 3, 1833— the tables 

 being prepared for these alone, although the results of subsequent 

 observations are, I am persuaded, not less striking. My observa- 

 tions are made at 9 A. M. and 9 P. M. The proportions of sky 

 clear at the times of observation, are set down in tenths. About 

 one-day before an aurora, the sky usually begins to increase in 

 clearness. In the following results, reference was had only to 

 clearness as compared with the corresponding hour of the prece- 

 ding day, and only to mean results. During the 24 hours prece- 

 ding the morning of the day on the evening of which the aurora 

 occurred, the sum of the increments of clearness was to that of 

 the decrements as two to one.* During the 24 hours immedi- 

 ately preceding the aurora, the increments are to the decrements 

 as six to one. Similar results would be obtained by taking the 

 number of instances in which the clearness increased or dimin- 

 ished in case of different auroras, instead of the amount of tenths, 

 as above. Within the two days preceding an aurora, and on 

 some part of the night of it, we observe all the circumstances 

 preparatory to and connected with crystallizations in the high 

 regions, developing themselves ; such - as increasing atmospheric 

 pressure, increase of cold, and the disappearance of clouds. On 

 the other hand, during the day or tw-o succeeding it, are devel- 

 oped all those circumstances which attend a more advanced stage 

 and lower descent of the products, whether crystalline or melted ; 

 such as a diminution of atmospheric pressure and clearness, and 

 an elevation of the temperature and dew point. The latter 

 changes, occupying less time, are rhore rapid than the former, and 

 hence appear more striking. For example, during the 24 hours 

 succeeding an aurora, the decrements of clearness are to the in- 

 crements as 37 to 1. But this high ratio requires in reality to-be 

 further increased, in conformity with the principles above estab- 

 lished. For, the principal increase of clearness which occurred, 



* The Slim of the tenths whioji respectively express the amount by which the 

 sky became clearer on the respective days immediately preceding the different au- 

 roras, is called, in expressing the mean results, the sum pf the increments during 

 the 24 hortrs immediately preceding </te aurora. A similar expression is used for 

 other epochs and for the decrements. 



