94 P. E. Chase on Mechanical Polarity. . 
Sabine’s Diagrams, Toronto Obs., vol. iii, plate 2), and the prob- 
able, if not certain, dependence of the variations of lon g period 
upon trade-winds (supra, Exp. 19-24) and planetary positions 
(Sabine and Wolf, loc. cit.), the hypothesis of any peculiar mag- 
netic zether, electric currents, or specific solar and lunar mag- 
netism, to explain the normal perturbations of the needle, appears 
to be entirely superfluous and unphilosophical. Every particle 
of the earth’s atmosphere is continually receiving and imparting 
the heat which is radiated from the earth and sun, its specific 
santa constarttl eng in such manner as to rt in- 
cessant rapi 
aetatiunh is counterbalanced iy terrestrial attraction, ones cal 
forcibly where the sun is in the horizon, and with the least 
relative efficiency when the sun is in the zenith (or ye sie in 
the summer solstice, provided the station is oe tropical). 
The pressure thus exerted varies from 0 ib. to 15 tb. per square 
inch. ‘aking the mean (73 ib. per square — or 1080 ib. per 
square foot) as the average sees ibraling tendency, we have 4 
force nearly fifteen times as great as that which produces, and 
more than Se: times as een as that which is prod oleae 
: sane and other mete- 
appears to be complete and aeecion usive. 
It is possible that a aie! study of the relation of the winds 
to we various —— variations would brin light other 
The earth’s most powerful radiation is dadiial, di in radial lines ; next in’ capes 
sity is the — towards the thermal poles, or ‘aon the a ’ meridians ; 08 
the i isothermal lels, the radiation is comparatively ins 
ely 1 
* The morning and evening maxima, and moon minimum eee) Shik 
combined pub totatita, are the principal causes of the daily barometrig = 
