On Recent Improvements in Electric Lighting. 57 



Dynamo machine of the ordinary type ; and where a 

 number of machines are required at the same spot,, one 

 exciter serves for the whole number. Still further improve- 

 ments have been made by dividing the commutator into 

 different branches, so that by increasing the number of 

 collecting brushes the current may be drawn off in 

 various circuits, each one being quite distinct and capable 

 of maintaining from one to ten lights on each circuit. 



We have now to examine the various forms of lamps that 

 have been designed from time to time for use with the gene- 

 rators of the current. 



Probably the earliest form may be considered as a stand 

 into which two pencils of carbon or graphite could be fitted 

 and remain insulated from each other. 



As the carbons were consumed they were adjusted by 

 hand ; very soon mechanical contrivances were introduced 

 to effect this automatically, but it is not too much to say that 

 although very many beautiful pieces of apparatus are in use 

 for this purpose, and considerable ingenuity has been dis- 

 played in designing the various forms, much still remains to 

 be done in this direction. For instance, Mr. Preece, on being 

 examined before the Select Committee of the House of Com- 

 mons, stated, in reply to a question as to the application of 

 the electric light for the use of the General Post Office, "that 

 at that time (1st July, 1879) he had not been able to determine 

 on a suitable form of lamp for their requirements, which were 

 of a special character. For his purpose he required each 

 light equal to 1000-eandle power; it must be absolutely 

 steady, so as not to fatigue the eyes of the operators in the 

 Telegraph Department ; and that it must remain steady and 

 uniform for at least nineteen hours without requiring any 

 attention whatever. Not any of the lamps he had 

 examined fulfilled all these conditions, but some had 

 especial qualifications. The Serrin gave the requisite 

 amount of light, the Werderman was perfectly steady, 

 and the Wallace-Farmer sufficiently durable. It is, however, 

 over eighteen months since this report was made, and much 

 progress has been made lately in improving and introducing 

 new forms of lamps. It will be unnecessary to take up 

 much of your time by describing or attempting to describe 

 the immense variety of lamps that have been brought 

 forward. It will suffice to mention those that have 

 apparently met with the greatest success for direct 

 lights — that is, a single light supplied by a continuous 



