90 Physical Discovery. 
range of mercury 32°, greatest range in one day 18°. In the be- 
ginning, I kept no column for variable winds. I think about twenty 
days should have been marked thus; the wind rarely blows an en- 
tire day from the west, but it did on the 18th of May. The south 
winds in the spring, are very dry, hot, and oppressive, and generally 
blow with considerable violence. It is a fact that the more open your 
house is kept during their prevalence, the higher will the mercury 
rise in the thermometer. ‘The trades,’ as will be observed, are the 
prevailing winds, and under their influence, the weather is never op- 
pressive, although the mercury may be at 90°; they range from N. 
E. toE. We have the ‘northers’ from October until March; they 
are always cold, generally attended with rain in the beginning, usu- 
ally last three days, and blow with considerable violence. They in 
fact bring the little rain we have during winter, beginning generally 
at S. W. they change in a couple of hoursto W.N.W.&N. The 
rain commencing at W. 
Art. XI.—Physical Discovery.—(Retrospective.)— The Magnetic 
Needle made to indicate the true North, and rendered more steady, 
by a newly invented Magnetic process. 
Extracted and translated from the Avant-Coureur, of Monday, June 10, 1771.—No. 
23; by Gen. H. A. 8S. Dearzorwn, and by him communicated for this Journal. 
Tue actual declination of the Magnetic Needle, from the true 
north, as indicated by this false guide, amounts to nearly twenty de- 
grees, and thereby deprives the common Mariner’s Compass of the 
general and daily advantages of that instrument, which should be in 
fact a portable horologe, and indicate with exactness the meridian 
line. ‘The author of the new edition and translation of Pliny the 
Naturalist, announced in one of the last numbers of the Avant-Cour- 
eur, has devised and executed a very curious magnetic process, 
which represses the north west deviation of the magnet, or rather, 
which compells nature, in one of her most mysterious laws, to over- 
come a kind of impotency in the magnetic needle, which, for a cen- 
tury has not allowed it, in the compass, to indicate the true north. 
This process consists in magnetizing two needles, one of which should 
be, but about half the size of the other. ‘They are proved seperate- 
ly, by placing them successively on a pivot, and causing them to gy- 
rate for some time, until it is ascertained, by various experiments, 
that they are magnetized, and that one end of each of them, is di- 
