ELECTRIC LIGHTING. 79 



Hall of Birmingham, and many times to my pupils at the 

 Birmingham 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, form- 

 ing 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 be- 

 fore filling with mercury, and allow some of the potash so- 

 lution 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 observations I have made lead me to believe 

 that when the carbon stick is incandescent in an atmos- 

 phere 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 was arranged for intensity, 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 is a 

 hopeless source of power, and that magneto-electric ma- 

 chinery driven by steam-power must be used. I fully con- 

 curred 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 



