448 
conducting wires orelectrodes. Theinner end of this tube 
is closed by a flat keel of solid glass, but the wires pass 
through this into the upper part of the bulb, where they are 
connected by an electrotype of copper toa fine loop or arch 
of carbonised woody fibre cut from the silicious skin of the 
bamboo cane. Mr. Edison exhibits specimens of bamboo 
from China, Japan, and South America, as well as fibres 
from Brazil, which he has tested in seeking a good and 
durable carbon for his lamp. He shows also a number 
of samples of the carbonised loops made by simple 
charring in a crucible or by treatment after the Ber- | 
thollet process, as well as loops of pure graphite very 
carefully cut. What the particular bamboo is that he has 
finally adopted we have never been able to learn, but it is 
probably a variety of the “ Shikakuahikee” of Japan, 
which yield a very close and even skin. The carbon 
loop is about 2} inches high, and 1 inch wide, and is so 
fine that its electric resistance is about 100 ohms. in the 
“16-candle lamps,” and about 50 ohms. in the 8-candle 
lamps. All the lamps at the Crystal Palace are plain 
single loop lamps ; but sometimes Mr. Edison combines 
two or more loops, as shown in Figs. 4and5. These loops 
can either be coupled up “in series,” or “quantity,” and 
NATURE 
[March 9, 1 882 
instead of making the loops plain they may be curled into 
a spiral form, ‘lhe air being exhausted from the bulb 
there is no oxidation of the carbon after a short time 
and Mr. Edison claims that his lamps will last 1oce 
|hours. This at an average rate of between three and 
four lighting hours per night would give a life of nine 
|months to each lamp; but the estimate may be found a 
little partial in practice : for though the carbon does no 
burn, it is doubtless slowly dissipated by the wasting 
|action of the gases and the energy of the current. As 
Mr. Edison claims to make the lamps at a shilling each, 
their durability is not so very important as it might at 
first appear. The Edison dynamo electric machine con- 
sists of two vertical electromagnets inclosing between 
their lower pole pieces of soft iron, a revolving arma- 
ture. In the armature the usual coils of insulated wire are 
replaced by longitudinal bars of copper of trapezoidal 
section insulated from each other by brown paper. These 
bars are connected to the slips of the commutator in such 
a manner as to give a continuous circuit through the bars 
and a continuous current to the brushes when the arma- 
| ture revolves. The main conductor conveying the current 
‘from the machine consists of a solid rod of copper in 
cross-section, like a segment of a circle. Two of these 
rods, the outgoing and return wire, are inclosed a little | 
apart in the same iron pipe and insulated by a black | 
compound resembling Thomson’s wax. Branch-con- 
ductors in the form of cables for side-streets are con- 
nected to the mains in a joint-box shown in Fig. 6. This 
consists of an iron box in which the mains are connected 
to two iron terminals. One branch cable is connected to 
one of these terminals direct, and the other through a short 
piece of lead to the other terminal. The lead acts as a 
safety-valve in fusing if the current is too powerful. The 
box is hermetically sealed, to keep the inside dry. The 
conductors led into the houses are of a still smaller size, 
having a diameter of from two to three millimetres; but 
throughout the whole system the going and returning 
wires keep together, and the lamps are simply connected 
across between them. In each lamp, too, there is a 
similar safety connection of lead to protect the carbon if 
the current is too strong, 
The incandescent system has evidently been brought 
to great perfection by Mr. Edison, backed as he is by 
plenty of capital and skilled assistance. Although the 
idea of it is not new, and was patented in England by 
Mr, Starr in 1845, Mr. Edison deserves great credit for 
Fic. 6. 
working it out in so practical a form. Starr described a 
vacuous bulb of glass containing a thin rod of carbon 
rendered incandescent by the passage of the current, and 
Mr. Edison found in this the rough pebble which he has 
cut and polished with so much success. Moreover, he 
saw the merits of the incandescent system for domestic 
lighting at a time when other electricians were giving all 
their attention to the arc light; and therein showed his 
genius and foresight. For it is evident now to electricians 
that while the arc light is well enough adapted for the 
lighting of large areas, it is unsuitable for small inte- 
riors. The practical success of Mr. Edison’s system is not 
thus far a complete justification of his early promises, for 
the cost is still an unknown quantity, as far as the public 
are concerned, and there are strong reasons for believing - 
that it will not nearly be so low as the startling figure held 
out in 1878. 
NOTES 
AT the annual meeting of the Geological Society the medals 
were presented as follows :—The Wollaston Gold Medal to Dr. 
Franz Ritter von Hauer, Director of the Austrian Geological 
Survey; the Murchison Medal to Prof, Jules Gosselet, of Lille 
