Natural Fhihsophy.—Metem’ology, 185 
2. The combined influence of all the iron is concentrated into 
a focus, the principal S. pole of which being upward in the N. 
Hemisphere, is situated in general near the middle of the upper 
deck. 
3. This focus of attraction, which appears to be a S. pole in 
N. dip, attracts the N. point of the compass, and produces the 
deviation in the needle. 
4. This deviation varies with the dip of the needle, the posi- 
tion of the compass, and the direction of the ship‘’s head. It 
increases and diminishes with the dip, and vanishes at the mag- 
netic equator. It is a maximum when the ship’s course is W. 
or E., and it is proportional to the sines of the angles between 
the ship’s head and the magnetic meridian. 
5. A compass placed in either side of the ship’s deck, direct- 
ly opposite to the focus, gives a correct indication on an E. or 
W. course, but is subject to the greatest deviation when the 
ship’s head is N. or S, 
METEOROLOGY, 
12. Sir H. Davy's Theory Mists » — According to this emi- 
nent chemist, land and water are cooled after sunset in a very 
different manner. The impression of cooling on the land is li- 
mited to the surface, and is very slowly transmitted into the in- 
terior ; whereas in water the upper stratum, when cooled, de- 
scends, and has its place supplied by warmer water from below. 
The surface of the water will therefore, in calm and clear weather, 
and in temperatures above 45* Eahr., be warmer than that of 
the contiguous land ; and consequently the air above the land 
will be cooler than that above the water. When the cold air, 
therefore, from the land mixes with that above the water, both 
of them containing their due proportion of aqueous vapour, 
a mist or fog must be the result. PhiL Trans. 1819, Part I. 
II. CHEMISTRY. 
13. New Alkali discovered hy MM. Pelletier and Caventou in 
the Veratrum Sahadilla . — In the prosecution of their researches 
respecting animal substances that have a decided action on the 
animal economy, these able chemists have discovered in the 
