30 
POPULAR SCIENCE REVIEW. 
The Rapieff burner, now employed in the “ Times ” publishing 
office, shows great mechanical ingenuity, and presents the great 
advantage that it can be sustained for a whole night without 
change of carbons or attendance, and without alteration of in- 
tensity, as the current always passes through the same length of 
wick. This wick consists, not of two, but of four, pencils opposed 
to one another in pairs, the upper fed by the positive, the lower 
by the negative current. The four carbons form the figure X, 
except that the lower pair is set in a plane at right angles to 
the upper. As the points consume away, the carbons are made 
slowly to approach each other, so that the arc is always of the 
same width, and keeps its fixed position in space. They are 
directed towards each other over small pulleys by a counterpoise 
of about three pounds sliding down the stem of the instrument. 
In another form, the four carbons are all inclined to each other 
at a variable angle, and a cylinder of lime is supported over the 
light, which, becoming luminous, increases the illuminating 
effect by about 40 per cent. The Rapieff also places a safety 
apparatus under each regulator, which is simply an automatic 
arrangement for allowing the current to pass to the other 
lamps in the same circuit, should one lamp happen to become 
extinguished. There are six lamps in circuit at the “ Times ” 
office, but Mr. Rapieff has successfully exhibited as many as 
ten. The dynamic machines of Gramme are used as excitors. 
The Werdermann light depends on a totally different principle. 
When in an electric lamp, electrodes having the same sectional 
area are used, the changes at the points between which the 
voltaic arc passes take place by a crater or hollow forming in 
the positive electrode which emits the light, the crater itself 
being heated by the current to white heat, and the surrounding 
part to redness. The negative electrode assumes the form of a 
cone, is only heated to redness, and emits scarcely any light. 
It is found, however, that an increase in the sectional area of 
the positive electrode diminishes the light emitted by that elec- 
trode; and if the increase be gradually continued, the light 
disappears entirely, while the heating effect upon the negative 
increases until it emits light. On the other hand, by increasing 
the sectional area of the negative electrode, the heating effect 
decreases proportionally to the increase of its area, until the 
heat almost entirely disappears, and the consequent consump- 
tion of that electrode is scarcely appreciable. The light given 
out by the positive electrode, on the contrary, increases in pro- 
portion to the difference between the sectional area of the two 
electrodes ; and instead of a crater being formed in the positive 
carbon, this assumes the form of a cone such as before occurred 
to the negative. The greater the difference between the areas 
of the two carbons, the less is the length of the voltaic arc 
