458 ‘yar Analyses of Books. -° ~~~ *—Dre. 
ed the effect. On the bar being inverted, so that the north pole 
was upward, the magnetism was very nearly destroyed by a 
single blow ; while two blows changed the poles. Hammerin 
the end of the bar in the plane of the magnetic equator also 
destroyed the polarity; but the effect was not fully produced 
until many blows had been struck. : 
‘“« When the poker had been previously hammered in a verti- 
cal position, an increase of magnetic effect on the bar was 
obtained, a single blow being now sufficient to enable the bar to 
lift about 20 grains ; and when the end was hammered into a 
kind of cup, so as to be easily bruised, the bar was by one blow 
rendered capable of lifting between 30 and 40 grains. After 10 
blows, the highest effect obtained in all the experiments was 
produced, the same bar readily lifting a nail of 188 grains, being 
nearly one-third of its own weight ! 
“The magnetism by percussion was found by subsequent 
experiments to be augmented when the length of the bars was 
increased ; thus a quarter-inch cylindrical bar of steel five inches 
long, after receiving 20 smart blows, produced a deflection of 
the needle, at the distance of three inches, of 13°, and lifted 64 
grains. Another piece of the same bar 7 inches long, after 
similar treatment, produced a deviation of 24°, and lifted 45 
grains ; and a third bar of the same kind 12 inches long, after 
90 similar blows, occasioned a deviation of the compass of 33°, 
and easily lifted 88 grains. The shortest bar, it was observed, 
received the full effect by the first two blows; but the others 
continued to increase in energy as the percussion was continued, 
These bars did not receive a power equal to that first used; the 
cause was probably their greater hardness. 
“3. A strong magnet properly tempered was injured in what- 
ever position it was hammered, but most rapidly when the north 
pole was upward. After no further diminution of its magnetism 
could be produced with the south end upward, a quick loss of 
ower was effected by hammering it with the north pole upward. 
But after the magnetism had been reduced to a certain extent 
by hammering im both positions, the power became nearly sta- 
tionary ; so that on striking it im any position with the same 
hammer, very little change of intensity occurred.” 
Besides these results, the author mentions the effect of pereus- 
sion on soft steel magnets, on soft iron not magnetized, and on 
cast iron. One of the Jirst capable of lifting upwards of 1000 
rains, when placed vertically upon the poker with its north pole 
upward, had its magnetism destroyed by five blows. A bar of 
soft iron of the same size and form as the steel bar first described, 
and weighing about 600 drains, was hammered for a considera- 
ble time while held vertically upon the poker. The greatest 
effect which he could produce with the large hammer was a 
deflection of the compass needle, at the distance of three inches, 
of 15 degrees. In this state it lifted a nail of 64 grains, but 
