314 Scientific Intelligence. 



for principally at the surface of the electrodes, though not 

 necessarily confined entirely to it. It is shown that light favors 

 the union of sulphur and silver to form silver sulphide, and it is 

 suggested that the same influence which would assist the union 

 of two substances when they have a tendency to unite might act 

 conversely when they have a tendency to separate. Radiation, 

 therefore, acting upon a thin layer of silver sulphide might exert 

 a material influence upon the conductivity of the sulphide by 

 facilitating the molecular rearrangement of the atoms of sulphur 

 and silver. The bearing of all this upon the explanation of the 

 action of light on selenium is obvious, though experimental proof 

 is needed to establish it. 



2. Molecular Shadows in Incandescent Lamps. — The forma- 

 tion of metallic deposits in incandescent lamps with a carbon 

 filament is described by J. A. Fleming, the metal coming from 

 the wire to which the carbon is attached. A sage-green deposit 

 of copper is observed in an Edison lamp not infrequently; and in 

 one case a silvery transparent metallic film of platinum was 

 deposited on the inside of the glass bulb. These deposits recall the 

 experiments of Wright (this Journal, xiii, 49 ; xiv, 169, 1 877), who 

 formed brilliant specula by deposition from a metallic electrode in 

 exhausted tubes. An interesting point in the lamp deposits was the 

 existence, under some circumstances, of a line of no deposit on the 

 surface in the plane of the filament. This is to be regarded as 

 the shadow of the loop in which the trajectory of the molecules 

 is interfered with by the carbon filament. The deposit near the 

 neck of the bulb is thicker than at the crown because of the 

 greater number of molecules which here strike the glass. In the 

 case of the carbon deposit, often observed, it was found that the 

 molecular shadow of the filament, or the line of no deposit, could be 

 formed by suddenly raising the filament to a very high tempera- 

 ture, as for instance by placing a 50-volt lamp for an instant on a 

 100-volt circuit; but when the deposit went on slowly no line 

 was observed, only a general smokiness. In the former case the 

 projection of the molecules from the carbon is violent enough to 

 prevent their paths from being altered by collision with molecules 

 of the residual air, so that a larger proportion reach the envelope 

 in the direction of projection, thus causing a deposit on all parts 

 except as shielded by the loop. The best shadows were obtained 

 from a lamp with a single loop. — Phil. Mag., August, 1885, pp. 

 141-144. 



3. Disintegration of the carbon filament in an incandescent 

 Electric lamp. — Some experiments carried on by Buchanan, 

 having as their object the deciding of the question as to whether 

 the observed breaking of the carbon filament at the negative end 

 was due to a local excess of temperature or a "Peltier effect," led 

 to a negative result ; the local heating detected being too small 

 to account for a break at one end rather than the other. The 

 author concludes that the disintegration of the carbon filament 

 preceding complete destruction, as described by Preece, is doubt- 



