158 Electric Lighting . [February, 
Birmingham, and many times to my pupils at the Birming- 
ham and Midland Institute. 
These exhibitions suggested an explanation of the mys- 
terious gaseous matter, which I believe to be the correct 
one, and also of the carbon deposit. It is this : — That the 
carbon contains occluded oxygen ; that when the carbon is 
heated some of this oxygen combines with the carbon, 
forming carbonic oxide and carbonic acid, and a little smoke. 
I proved the presence of carbonic acid by the usual tests, 
but did not quantitatively determine its proportion of the 
total atmosphere. 
If I were fitting up another tube on this principle I should 
wash it with a strong solution of caustic potash before filling 
with mercury, and allow some of the potash solution to float 
on the mercury surface, by filling the tube while the glass 
remained moistened with the solution. My objeCt would be 
to get rid of the carbonic acid as soon as formed, as the ob- 
servations I have made lead me to believe that — when the 
carbon stick is incandescent in an atmosphere of carbonic 
acid or carbonic oxide — a certain degree of dissociation and 
re-combination is continually occurring, which weakens and 
would ultimately break up the carbon stick, and increases 
the sooty deposit. 
The large battery above described was arranged for in- 
tensity, but even then it was found that the quantity (I use 
the old-fashioned terms) of electricity was excessive, and 
that it worked more advantageously when the cells were 
but partially filled with acid and sulphate. A larger stick of 
carbon might have been used with the whole surface in full 
aCtion. 
After working the battery in various ways, and duly con- 
sidering the merits of the other forms of battery then in 
use, Mr. Starr was driven to the conclusion -that for the 
purposes of practical illumination the voltaic battery was a 
hopeless source of power, and that magneto-eleCtric ma- 
chinery driven by steam-power must be used. I fully 
concurred with him in this conclusion, so did Mr. King, 
Mr. Dorr, and all concerned. 
Mr. Starr then set to work to devise a suitable dynamo- 
eleCtric machine, and, following his usual course of starting 
from first principles, concluded that all the armatures hith- 
erto constructed were defective in one fundamental element 
of their arrangement. The thick copper-wire surrounding 
the soft iron core necessarily follows a spiral course, like 
that of a coarse screw-thread ; but the eleCtric current or 
lines of force which it is designed to pick up and carry circulate 
