New-York tribune., 1903-01-11
THE MERCURY VAPOR LAMP.

American electricians have been familiar for
nearly two wears with Cooper Hewitts mercury
vapor lamp, and can well understand the en-
thusiasm with which Lord Kelvin and other
British experts regarded it when it was first
shown TO them last Friday. Several theoretical
and practical questions concerning the inven-
ton are not fully solved. Possibly Mr.. Hewitt
does not himself believe that it has reached its
full development in every detail. But as 1t
stands to-day his lamp represents a degree OF
originality and an amount of experiment and
calculation which have inspired hearty admira-
ton in those who best understand the device
and the work of which it is the outcome.
In outward form Mr.. Hewitt's lamp reminds
one of the Gessler tube. Macfarlane Moore's
beautiful demonstrations six years ago and
some of the marvellous exhibitions of Mr..
Tesla. In these, however, the effects were Sc
cured by rapidly alternating or interrupted high
pressure currents. Both the means and the
principle were different from those employed
in the mercury vapor lamp In the latter the
gas is made incandeScent, as is Mr.. Edison's s
carbon ilament, simply by resistance to the
current going through it and by heating in con-
sequence. For this service low pressure con-
tinuous current is sufficient. There is no In
duction or wave phenomena or "electrostaHc
discharge
From the popular point of view the device
possesses several merits. The apparatus is sim
pie, and light is obtained almost Immediately
upon turning on the current In both respects
the Hewitt system seems superior to the Nernst
system, another recent candidate for favor.
There has been some question as to the color Of
the glow emitted. But a violet tinge is less OBJ
jectionable TO most people than the greenish
light which characterized the early Welsbach
1cfI 91xx h.
trely corrected just as the latter has been.
One of the most important recommendations of
the mercury vapor lamp is its economy Mr.
Hewitt believes that he gets given amount of
light by the expenditure of only one-third of
the energy required by the arc lamp, and from
one-eighth to one-tenth of that consumed by the
incandescent lamp. If these estimates are fully
sustained by later tests radical Improvement
in at least one respect will have been secured
1t remains to be discovered, of course, how the
lamp itself will compare with the arc and in
candescent lamps in cost, and how often it will
need renewal. On the whole a favora BILE show
ing on these points may be expected Almost
the only other consideration then remaining
viii be the possibility of developing after long
trial, defects now unforeseen either in outdoor
illumination, to which it is best adapted per-
haps, or in offices and households.
Electrical engineers Will feel more interest
than the general public in Mr.. Hewitt's other
new invention mentioned in recent London
dispatches. When low tension direct cur
rent such as was once universally used for the
Edise1i lamp, is available Mr.. Hewitt needs no
extra apparatus. There is a growing tendency
to-day, however, to generate electricity for dis
tribution in the form of an alternating current,
and subsequently to change this into a direct
current. The Manhattan Elevated Railway
Company does So for instance and in it's sub
stations machine that looks like dynamo
but is called a rotary converter. There is likely
10 be growing demand in lighting well as
traction service. therefore for apparatus per-
forming this function; and it is not incredible
that the old converter will be surpassed. Until