‘ 
May 5th, 1871.] 1 21 (Chase. 
On the relation of the AURORAS TO GRAVITATING CURRENTS. 
By Purny EARLE CHASE. 
(Read before the American Philosophical Society, May 5th, 1871.) 
Prof. Loomis’s observations of the number of Auroras in each month 
of 1869 and 1870 (Amer. Jour. of Science, 3d S., i, 309), are specially 
noteworthy, both because. of the careful accuracy of the observer, and 
because they are the first published observations which furnish satisfac- 
tory data for an approximate determination of the laws of auroral dis- 
tribution. : 
If the auroras are, as is now generally believed, luminous manifesta- 
tions of terrestrial magnetism, it seems reasonable to look to them for 
some additional evidence upon the question of the relation between mag- 
netic and gravitating currents. Messrs. Baxendell and Bloxam have al- 
ready pointed out some resemblances between hyetal and magnetic curves, 
(see Proce. A. P. 8., x, 868) and if analogous resemblances can be traced 
between hyetal and auroral curves, they will be interesting and suggestive. 
T have not found the similarity between the annual distribution of rain- 
falls and of auroras, sufficiently striking to impress any one who has not 
made a special study of the causes of resemblance and difference. But, 
as I have repeatedly urged, currents are subject to an increased number 
of disguising disturbances, in proportion to the sluggishness of their mo- 
tion, and the time which is consequently required for their formation or 
change. We may very reasonably look for analogies between the daily 
and the aunualauroral or magnetic curves, of a character for which we 
could hope to find no parallel in wind, rain, or ocean-current curves. 
If we desire, therefore, to find evidence of the joint influence of solar 
expansion and gravitating equilibrium, we should look where it is most 
likely to be found, and to the best of the observations which may be sup- 
posed to be fairly comparable. There are similar variations of solar at- 
titude, and consequently increasing and diminishing solar foree, in the 
day and in the year, but the effects of these variations upon the precipita- 
tion of vapor, are more likely to be shown in their greatest simplicity, by 
the meaus of observations at different hours of the day than at different 
seasons of the year. I know of no published observations of this char- 
acter at New Haven, but there are some extending over a long series of 
years, at Philadelphia and at Greenwich, the curves at each station indi- 
cating minima of rainfall at noon and midnight, and maxima in the 
morning and evening. The difference of longitude between Pihiladeiphia 
and New Haven being less than 2$°, it is not likely that there is any 
material difference in the daily rain-curves at the two places. 
In order to make the curves fairly comparable, both in regard to the 
times and the magnitudes of deviation, I treated the auroral observations 
in the same manner as those of rainfall (Proc.. A. P. 8., x, 526). Both 
in the magnetic and in the hyetal phenomena, the greatest effects accom- 
pany the greatest atmospheric changes, But in the magnetic disturb- 
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