Experiments and Obfervations . 25 
put about four ounces of iron filings. Things being thus diT- 
pofed, and left undiflurbed for about half an hour, the needle 
remained unaltered. Then the pieces of magnetic fleel and 
earth were flirred with a flick, in confequence of which the 
needle was agitated. After this, fome diluted vitriolic acid was 
poured upon the filings in one of the vefifels, the action of 
which attracted the needle that way ; but whilfi: the needle 
remained in that lituation, fomc? diluted vitriolic acid was 
poured upon the iron filings in the other veflel, which flood on 
the other fide, in confequence of which the needle went back 
again towards its former direction. Whilfi the effervefcences 
were going on in the two veffels, the magnet in the firfl veflel 
was heated by means of boiling water, which occafioned ano- 
ther alteration in the direction of the magnetic needle ; and 
thus, by altering the flate of the ferruginous fubflances in the 
vefifels, the needle’s dire&ion was altered, in evident imitation of 
the natural variation. 
T. CAVALLO. 
\ 
Vo l. LXXV 1 I. 
E 
