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 (he 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, 5 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 5 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 hours to W. N. W. & N. The 

 rain commencing at W. 



Art. XL — 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. S. Dearborn, and by him communicated for this Journal. 



The 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- 



