“Magnetism as Test for Iron. 393 
vegetable physiology, and as enabling the lovers of flowers to 
prolong, for a day, the enjoyment of their short-lived beauty. 
Most flowers begin to droop and fade, after being kept during 
twenty-four hours in water ; a few may be revived by substituting 
fresh water ; but all (the most fugacious, such as the poppy, and 
perhaps one or two others, excepted) may be completely restored 
by the use of hot water. For this purpose place the flowers in 
scalding water, deep enough to cover about one-third of the 
length of the stem; by the time the water has become cold, the 
flowers will have become erect and fresh ; then cut off the coddled 
end of the stems, and put them into cold water. 
MAGNETISM APPLIED AS A TEST FOR IRON. 
The third Number of the New Series of the Annales des Mines 
contains a paper of M. Haiiy on the means of detecting iron in 
mineral or other substances by magnetism. Its presence is 
ascertained by the attraction of the substance, either immediately 
or after having been heated in the flame of a taper, on the mag- 
netic needle ; but in order to make the effect more sensible and 
evident, M. Haiiy has taken advantage of the combined forces of 
the magnetism of the earth and of a bar magnet acting simulta- 
neously on the needle. 
The needle should be of excellent steel, and highly magnetic, 
its cap should be made of agate or rock crystal, and the point on 
which it moves very fine. If such a needle be left to itself it will 
staud parallel to the magnetic meridian, in consequence of the 
forces exerted on it by the magnetic poles of the earth ; and if 
from any cause the needle is deflected from this line, the force 
exerted upon it to bring it back to its first position will be as the 
sine of the angle which the needle makes with the magnetic me- 
ridian. The power, therefore, which tends to return the needle 
to its first position, increases until it has passed through a quar- 
ter of a circle, and then decreases again ; but the increase is ina 
decreasing ratio, and the decrease is in the increasing ratio; and 
supposing the needle to be moved through 90° by nine succes- 
sive additions of force, it would require the greatest addition to 
move it from 0 to 10°, and the least to move it from 80 to 90° ; 
and then if the power which moved it from 80 to 90° carry it 
over that point, it would be more than sufficient to make it tra- 
verse the next quadrant, because the forces exerted by the earth’s 
magnetism continually decrease. 
In order to take advantage of this circumstance, let the needle 
be influenced only by the earth’s magnetism, it will stand paral- 
lel to the magnetic meridian; then if the south pole of a bar 
magnet be approached towards the similar pole of the needle, 
the bar being in a line with the needle, a repulsion will take 
place, 
