Fan. 11, 1883 | 
But more than this, not only does the train take off current 
from the section 1 when it is just leaving it, and entering section 
2, but no following train entering section I can receive current 
or motive power until the preceding train has entered section 3. 
[Experiments were then shown proving that with this system a 
following train could not possibly run into a preceding train even 
if the preceding train stopped or kacked.] Now why does the 
following train when it runs on to a blocked section pull up so 
quickly? The reason is because it is not only deprived of all 
motive power, but is powerfully braked, since when electricity 
is cut off from a section, the insulated and non-insulated rail of 
that section are automatically connected together, so that when 
NATURE, 
257 
a generator short circuited on itself, producing, therefore, a 
powerful current which rapidly pulls up the engine. [Experi- 
ments were then shown of the speed with which an electromotor, 
which had been set in rapid rotation and then deprived of its 
motive current, pulled up when its two terminals were short- 
circuited. ] 
Whenever, then, a train, it may be even a runaway engine, 
enters on a blocked section, not only is all motive power with- 
drawn from it, but it is automatically powerfully braked, quite 
independently of the action of the engine-driver, guard, or 
signalman, No fog, nor colour-blindness, nor different codes of 
the train runs on to a blocked section the electromotor becomes 
signals on different lines, nor mistakes arising from the exhausted 
nervous condition of overworked signal-men, can with this system 
— 
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produce a collision. The English system of blocking is merely 
giving an order to stop a train; but whether this is understood 
or intelligently carried out is only settled by the happening or 
non-happening of a subsequent collision. Our Absolute Auto- 
matic Block acts as if the steam were automatically shut off and 
the brake put on whenever the train is running into danger ; 
nay, it does more than this—it acts as if the fires were pnt out 
and all the coal taken away, since it is quite out of the power of 
the engine-driver to re-start his train until the one in front is at 
a safe distance ahead. i bes 
But all trains will undoubtedly be lighted with electricity ; 
must, then, the train"be plunged into darkness when it runs on 
to a blocked section?to which no electric energy is being sup- 
5S 
plied? No! Ifsome of the electric energy supplied to a train 
when it is on an unblocked section be stored up in Faure’s 
accumulators, such as are at present used on the Brighton 
Pulman train, the lamps will continue burning even when the 
train has ceased to receive electric energy from the rubbed rail. 
When, then, we commit the carrying of our power to that 
fleet messenger to which we have been accustomed to entrust the 
carrying of our thoughts, then shall we have railways that will 
combine speed, economy and safety ; and last, but not least to 
us Londoners, we shall have the entire absence of smoke, the 
presence of which nearly causes the convenience of the Under- 
ground Railway to be balanced by the pernicious character of its 
atmosphere. 
SOC ETIES AND ACADEMIES 
LONDON 
F* RoyalfSociety, December 21, 1882.—‘‘ On the Origin of 
the Hydrocarbon Flame Spectrum.” By G. D, Liveing, M.A., 
F.R.S., Prof. of Chemistry, and J. Dewar, M.A., F-R.S., 
Jacksonian Prof., University of Cambridge. } 
In previous communications! to the Society we have described 
the spectra of what we believe to be three compound substances, 
viz., cyanogen, magnesium-hydrogen, and water. : 
In these investigations our chief aim has been to ascertain 
facts, and to avoid as far as possible adopting any special theory 
regarding the genesis of the spectra in question. 
Specific spectra have been satisfactorily proved to emanate 
from the compound molecules of cyanogen, water, and magnesium- 
hydrogen, so far as we can interpret in the simplest way the many 
observations previously detailed. The fact that a fluted spectrum 
is produced under certain conditions, by a substance which does 
not give such a spectrum under other conditions, is of itself a 
proof that the body has either passed into an isomeric state or 
has formed some new compound ; but we are not entitled to 
assert, without investigation, which of these two reasonable 
explanations of the phenomena is the true one. There is, how- 
ever, a spectrum to which we have had occasion to refer in the 
papers on the spectra of the compounds of carbon, which closely 
resembles that of a compound substance, and which we, in 
common with some other spectroscopists, have been led to 
attribute ito the hydrocarbon acetylene, without, however, being 
1 ‘*On the spectra of the Compounds of Carbon with Hydrogen and 
Nitrogen.” Iand II. Proc. Roy, Soc., vol. 30, pp. 152, 494. “On the 
Spectrum of Carbon,” 7., vol. 33, p. 403. ‘‘General Observations on the 
Spectrum of Carbon and its Compounds,” 7d, vol. 34, p. 123. ‘‘On the 
Spectrum of Water,”’ 7d., vol. 30, p. 480. and vol. 33, p. 274. ‘‘ Investiga- 
ions on the Spectrum of Magnesium,”’ 2., vol. 32, p. 189. 
f 
s' 
t 
able to bring forward such rigid experimental proofs of its origin 
as we have adduced in the case of the three substances above 
referred to. 
hydrocarbon flame spectrum is really due to a hydrocarbon was 
always indirect. 
carbon, such as those of hydrogen mixed with bisulphide of 
carbon or carbonic oxide, and the flame of cyanogen in air, did 
not give this spectrum, and these particular flames are known, 
from the investigations of Berthelot, to be incapable of generating 
acetylene under conditions producing incomplete combustion. 
On the other hand, we found that a flame of hydrogen mixed 
with chloroform, which easily generates acetylene, gives the 
hydrocarbon flame spectrum in a very marked manner, and it is 
known that the ordinary blow-pipe flame, in which the same 
spectrum is well developed, contains this hydrocarbon. 
In other words, the experimental evidence that the 
Thus, we showed that many flames containing 
These and other experiments point to the intimate relation of 
hydrogen and carbon in the combined form of acetylene to the 
production of this spectrum during combustion. 
observations on the spectrum of the electric arc taken in 
different gases, the flame spectrum was always noticed, and 
seemed to be independent of the surrounding atmostphere. 
the mode in which those experiments were conducted, it was 
easily shown that the carbons were never free from hydrogen, 
and that the gases always contained traces of aqueous vapour. 
Under these conditions acetylene is formed synthetically during 
in our various 
In 
he electric discharge, the line spectrum of hydrogen being absent; 
o that we were never convinced that the spectrum was not due 
o the former substance, 
It is well to remark in passing, that our previous work on the 
spectrum of the carbon compounds was mainly directed to that 
particular spectrum which is characteristic of the flame of 
cyanogen, and only indirectly to the flame spectrum of hydro- 
carbon. 
We were further supported in connecting the latter 
