280 MR. LUKE HOWARD ON THE INFLUENCE OF THE MOON’S DECLINATION, ETC. 
shown, as it is found to operate through a cycle of eighteen years. In these, the mean 
weight of our atmosphere increases through the fore-part of the period ; and, having 
kept for a year at the maximum it has attained, decreases again through the remain- 
ing years to a minimum ; about which there seems to be some fluctuation, before the 
mean begins to rise again. 
This result is brought out in different ways by all the averages upon years ; and it 
pervades, though with less of uniformity, those upon the quarter periods or weeks of 
declination. The study of these, with a' view to theory , rude and imperfect as they are, 
may become, I would willingly hope, an occupation for those more capable and better 
prepared than myself to grapple with the subject. 
L. H. 
February 3, 1841. 
