TROWBRIDGE. — IIKUI ELECTROMOTIVE FORCE. 2(»5 
that this variation in conductibility is sufficient to account for the phenomena of 
masking without recourse to a theory of electrons which provides for suitable damp- 
> ing of electrical oscillations. The electron theory may he an ultimate explanation, 
M-S 
however, of electrical conduction. 
I speedily found that the limit of resistance of glass tubes enclosing rarefied g: 
was low, and that it was impossible to utilize to its full extent the amount of energy 
which was at my command. Geissler tubes filled with o\\ en, hydrogen, and nitrogen 
all gave the same spectrum when sulliciently strong discharg I were passed through 
the tubes. This 
q 
tubes. It seems to be imp. sible to 
tubes and cleanse them to such a degree that high electromotive force and 
strong; heating effect will not drive off occluded gates or closely adhering layer* of 
o **~ o 
gases. It is not impossible, moreover, even if the surface layer of adhering ^ 4 
is removed, that it is replaced by gases coming from the interior 6f the glass. It 
is well known that glass holds water vapor in its mass, and quartz permits the passe 8 
of hydrogen when the quartz is incandescent. 
On account of the difficulty of leading platinum wire . air tight, into quartz v< Is, 
the ends of the quartz tubes which had been blown out into bulbs were carefully ground 
and were luted to glass bulbs by means of silicate of soda. The electrode* were led 
into the quartz bulbs as far as possible to avoid the volatilization of the Bilicate of 
sod 
of this volatilization from reaching the cap 
One of the most striking facts which the investigator in spectrum analysis meets 
1 
study of electric discharges through exhausted tubes is the difficulty of 
hich, h 
rid of impurities which arise from the methods of exhaustion. The mercury used 
in the process of exhaustion provides mercury vap»r. — v 
source of trouble, for it can be frozen out by liquid air. A more serious trouble 
arises from the lubrication of the valves of the pump. 'I 
rge 
aource 
of carbon monoxide, traces of which are rarely absent if rong discha. 
employed. Moreover, the substances used by chemists to dry gaaei are an unfailing 
source of impurities, which are revealed by the astonishing delicacy of spectrum 
analysis. 
The student who endeavors to obtain a spectrum of hydrogen with 
d 
charges is apt to become sceptical of conclusion based upon this delicate method 
of analysis, for he must confine his study to comparatively weak excitation of the 
rarefied hydrogen. The moment he employs a powerful dischar all trace of hydro 
;«n disappears, and he must conclude that there k some phenomenon of occlusion 
of chemical combination or masking. What astonishes one most, perhaps, is the 
