38 Mr. Joseph W. Swan [March 10, 



Literary and Pliilosophical Society of Newcastle in February, 1879. 

 The vacuum had been produced by Mr. Stearn by means of an im- 

 proved Sprengel pump of his invention. 



BLickening of the lamp glass, and speedy breaking of the carbons, 

 had been such invariable accompaniments of the old conditions of 

 imperfect vacua, and of imperfect contact between carbon and con- 

 ducting wires, as to have led to the conclusion that the carbon was 

 volatilised. But under the new conditions these faults entirely dis- 

 appeared ; and carefully conducted experiments have shown that well- 

 made lamps are quite serviceable after more than a thousand hours' 

 continual use. 



Here are some specimens of the latest and most perfected forms of 

 lamp. The mode of attaching the filament to the conducting wires by 

 means of a tiny tube of platinum, and also the improved form of the 

 lamp, are due to the skill of Mr. Gimmingham. 



The lamp is easily attached and detached from the socket which 

 connects it with the conducting wires ; and can be adapted to a great 

 variety of fittings, and these may be provided with switches or taps 

 for lighting or extinguishing the lamps. I have here a lamp fitted 

 especially for use in mines. The current may be supj^lied either 

 through main wires from a dynamo-electrical machine, with flexible 

 branch wires to the lamp, or it may be fed by a set of portable store 

 cells closely connected with it. I will give you an illustration 

 of the qualify of the light these incandescent lamps are capable of 

 producing by turning the current from a Siemens' dynamo-electric 

 machine (which is working by means of a gas engine in the 

 basement of the building) through sixty lamps ranged round the 

 front of the gallery and through six on the table. (The theatre was 

 now completely illuminated by means of the lamps, the gas being 

 turned off during the rest of the lecture.) 



It is evident by the appearance of the flowers on the table that 

 colours are seen very truly by this light, and this is suggestive of its 

 suitability for the lighting of pictures. 



The heat produced is comparatively very small ; and of course 

 there are no noxious vapours. 



And now I may, I think, fairly say that the difficulties encountered 

 in the construction of incandescent electric lamps have been com- 

 pletely conquered, and that their use is economically practicable. In 

 making this statement I mean, that, both as regards the cost of the 

 lamp itself and the cost of supplying electricity to illimmiate it, light 

 can be produced at a cost which will compare not unfavourably with 

 the cost of gas light. It is evident that if this opinion can be sus- 

 tained, lighting by electricity at once assumes a position of the widest 

 public interest, and of the greatest economic importance ; and in view 

 of this, I may be permitted to enter with some detail into a considera- 

 tion of the facts which support it. 



There has now been sufficient experience in the manufacture of 

 lamps to leave no doubt that they can be cheaply constructed, and wo 



