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liant : the charcoal scintillated like steel or iron. 1 never 

 before observed these scintillations in the combustion of char- 

 coal. Coke points were also ignited, and a most intense light 

 produced ; but during the experiments with the coke points 

 the circuit was interrupted in consequence of the fracture of 

 one of the porous cells, which caused the dilute and concen- 

 trated acids to mingle together, and, consequently, to boil 

 over, until the porous and cast-iron cells were nearly emptied. 

 Notwithstanding this interruption of the circuit, the arc of 

 light between the coke points was about an inch long, and 

 the heat of the flame deflagrated a file. 



*' I had arrangements made for a long series of experi- 

 ments on the decomposing power of the voltaic current, and 

 of voltaic heat, and on the illuminating power of the various 

 kinds of voltaic light, but these experiments I was obliged to 

 omit, through fatigue, exhaustion, and bad health. I have 

 since tried the illuminating power of the light produced by 

 the ignition of coke points; and for the gas microscope and 

 polariscope have found it far superior to the oxyhydrogen 

 lime light. With good coke points, abundant light for the 

 microscope and polariscope may be obtained from a battery 

 containing twenty-five cast-iron cells, and as many zinc plates, 

 each two inches by four : if the coke be not very good, forty 

 plates will be required. When an iron cell, two and a half 

 inches wide and four inches high, is large enough to contain 

 between it and the porous cell nearly a wine-glassful of the 

 concentrated acids, the battery will work with undiminished 

 power for about three hours without any additional acid. If 

 the cell containing the zinc plates be small, it will be neces- 

 sary to pour in a little dilute acid every half hour. I have 

 got the lime light by igniting the mixed gases as they were 

 produced by the decomposition of water, and throwing the 

 flame on lime. 



" Maynooth College, 

 ''Aprils, 1848." 



