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XVI. On Molecular Shadows in Incandescence Lamps. By 

 J. A. Fleming, M.A., D.Sc. (Lo?id.), Fellow of St. John's 

 College, Cambridge, Professor of Electrical Technology in 

 University College, London*. 



SINCE presenting a short note on the above subject in 1883 

 many further opportunities have occurred for observing 

 the conditions under which molecular shadows are formed in 

 incandescence carbon-filament lamps, and of correcting one or 



LINE OF 

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two statements then made. It has been observed in an immense 

 number of cases, that not only do incandescence lamps become 

 coated on the interior of the glass with a deposit of carbon, 

 but that the envelope may have deposited upon it a metallic 

 film, derived from the leading-in wires to which the carbon 

 filament is clamped. In the Edison lamp the platinum wire 

 only just passes through the glass, and is connected with 

 copper wires broadened out into a clamp ; the filament is 

 gripped in these clamps and then electro-plated over with 

 copper to effect a good junction. In the Swan lamp the 

 platinum wires are joined directly on to the carbon. It occa- 

 sionally happens that there is an unusual amount of resis- 

 tance at the clamps, or that by excessive electromotive force 

 more current is forced through the lamp and more heat gene- 



* Communicated by the Physical Society : read June 27, 1885. 



