IN MAGNETISM AND ELECTRICITY. 
107 
it at a considerable angle. When the electric lamp was placed at the top of a lofty 
building, the light evolved from it was sufficient to cast the shadows from the flames of 
the street-lamps a quarter of a mile distant upon the neighbouring walls. When viewed 
from that distance, the light was a very magnificent object to behold, the rays proceeding 
from the reflector having all the rich effulgence of sunshine. 
80. A piece of the ordinary sensitized paper, such as is used for photographic printing, 
when exposed to the action of the light for twenty seconds, at a distance of 2 feet from 
the reflector, was darkened to the same degree as was a piece of the same sheet of paper 
when exposed for a period of one minute to the direct rays of the sun, at noon, on a very 
clear day in the month of March. 
81. The extraordinary calorific and illuminating powers of the 10-inch machine are 
all the more remarkable from the fact that they have their origin in six small perma- 
nent magnets, weighing only lib. each (12), and only capable, at most, of sustaining 
collectively a weight of 60 lbs. ; while the electricity from the magneto-electric machine 
which was employed in exciting the electro-magnet was, of itself, incapable of heating 
to redness the shortest length of iron wire of the smallest size manufactured. 
82. The production of so large an amount of electricity was only obtained (as might 
have been anticipated by the physicist) by a correspondingly large expenditure of mecha- 
nical force, as the machine when in full action absorbed, as nearly as could be estimated, 
from eight to ten horse-power. When the 2-^-inch magneto-electric machine (58) was 
substituted for the 1-f-inch machine, in the combination before described (76), the 
magnetism developed in the electro-magnet of the 10-inch machine was exalted to such 
a degree that, although the strong leather belt from the main shaft, used for driving the 
countershaft, was 6 inches in width and acted upon a pulley 10 inches in diameter, it was 
scarcely able to drive the machine. 
83. It was, however, found, as in the case of the 5-inch electro-magnetic machine, that 
beyond certain limits a great augmentation of the magnetism of the electro-magnet was 
only attended by a small increase of electricity from the armature (65). The results of a 
number of experiments, in which various quantities of electricity were transmitted through 
the coils of the electro-magnet of the 10-inch machine, proved that when it was excited 
through the agency of the six permanent magnets, combined with the 5-inch machine, 
(76), the maximum amount of electricity from the machine, when working at a speed of 
1500 revolutions per minute, had been nearly obtained. 
84. It was also found that the maximum amount of power, as measured by the quan- 
tity of wire melted, was very nearly obtained from the 10-inch machine when its electro- 
magnet was excited by means of a 5-inch magneto-electric machine alone, instead of the 
combination of magneto-electric and electro-magnetic machines used for that purpose (76). 
85. When the electro-magnet of the 10-inch machine was excited by means of the 
2^-inch magneto-electric machine alone (58) (as shown on the wooden top of the machine 
in fig. 10), about two-thirds of the maximum amount of power from the 10-inch ma- 
chine was obtained. 
