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POPULAR SCIENCE REVIEW. 
in developing its powerful light, and in the heating and fusing 
of bars and wires of various lengths of different metals. This 
light as shown in the library presented most remarkable features, 
and was strong enough to make itself powerfully supreme over 
the brighest daylight of that period of the year — February. It 
was generated from stout carbon points over a foot in length, 
and half an inch square ; and when concentrated by a polished 
reflector, a beam of white light, 2 feet in diameter, issued forth 
glittering upon every object in its gradually widening path with 
more than the brilliancy of sunshine. Around the white central 
beam was an outer cylinder of bluish light, within the region of 
which, blue, violet, and mauve coloured ribbons and dresses ex- 
hibited the like exquisite intensification of hue as when under 
the rich rays of magnesium. Only one feature in the light was 
even seemingly at all objectionable, and this was a certain 
exceedingly rapid flicker ; but scarcely noticeable when the back 
was turned upon the source. This flicker is, however, peculiar 
only to this particular machine, and is not observable in the 
smaller 7-inch or 5-inch machines which have been made by 
Mr. Wilde ; it could be overcome in the present one by an 
acceleration of the speed of the armature from 1,500 to 2,000 
revolutions per minute, or by the use of a commutator to send 
the electrical currents in one direction. In no way is it a 
defect, for when the light is diffused out of doors, this tremu- 
lousness is not perceptible at a short distance away; as for 
example, when it was displayed from the top of Burlington 
House, the flicker was not noticeable at the gateway of the 
court-yard, where at night I distinctly read the small brevier 
print of one of the popular sixpenny editions of Cooper’s u Water- 
Witch,” and obtained distinctly the shadow of the flame of a 
lucifer-match on the back of my invitation card. The reason 
for not using a commutator, is that something of the force of 
the current would be lost ; opposite currents are therefore 
allowed to alternate at the carbon points with immense rapidity, 
and what we really see in the flicker of the light is the flash, 
first of a current downward from above, and then the flash upwards 
of a current from below. These reversals, accomplished 3,000 
times a minute, are appreciable by the optic nerves, but at 4,000 
times would not be so. It is, however, no defect, as we have 
said, in the penetration, volume, or practical value of the 
marvellous beam. It was also wonderful to see the actual flames 
dashing out around the incandescent points of the carbons. 
The spectrum of the arc of light between the carbons (which 
were kept by a Dubosq lamp within less than a quarter of an 
inch of each other), as seen through a Browning’s direct vision 
spectroscope, was most gorgeous, the lines of burning iron, 
sodium, and other impurities in the carbons coming out with the 
