1879.] on the Electric Liyht, 11 



of extraordinary power, and if an electric lamj) be introduced into the 

 common circuit of magnet and armature, we can readily obtain a 

 most powerful light.* By this discovery, then, we are enabled to 

 avoid the trouble and cx2)onse involved in the em2)loynicnt of per- 

 manent magnets ; we are also enabled to drop the exciting magneto- 

 electric machine, and the duplication of the electro-magnets. By it, 

 in sliort, the electric generator is so far simplified, and reduced in 

 cost, as to enable electricity to enter the lists as the rival of our 

 present means of illumination. 



Soon after the announcement of their discovery by Siemens and 

 Wheatstone, Mr. Holmes, at the instance of the Elder Brethren of 

 the Trinity House, endeavoured to turn the discovery to account. 

 Already, in the spring of 1869, he had constructed a machine which, 

 though hampered with defects, exhibited extraordinary power. The 

 light was developed in the focus of a dioptric aj^paratus placed on the 

 Trinity Wharf at Blackwall, and witnessed by the Elder Brethren, their 

 engineer, and myself, from an observatory at Charlton, on the oppo- 

 site side of the Thames. Falling upon the suspended haze, the light 

 illuminated the atmosphere for miles all round. Anything so sun- 

 like in si)lendour had not, I imagine, previously been witnessed. The 

 labour necessary to bring a machine of the kind to j^erfection was 

 then strikingly illustrated. It required a year of work after its first 

 successful performance to render the action of the machine secure. 

 There were ten electro-magnets and twenty helices in operation, 

 four of the latter being used to excite the electro-magnets, and the 

 remaining sixteen to develop the currents used for the light. When 

 thrown into action the strain produced by the mutual attraction of the 

 poles was so great as to endanger the stability of the machine, and to 

 lessen this defect it was many times taken asunder and constructed 

 anew. The machine was subjected to very severe scrutiny at Black- 

 wall, Mr. Ayres watching it constantly day and night during a con- 

 siderable number of trials. .Defects were revealed and removed, 

 the final result being expressed in the following brief extract from a 

 long rej^ort which I had the honour of submitting to the Elder 

 Brethren February 21, 1870: "I think the experiments prove that 

 with a due and by no means excessive amount of care, the dynamo- 

 electric engine of Mr. Holmes may be worked in a satisfactory manner. 

 With regard to the stability of the internal portions of the machine, 

 it is rather a question for your engineer (Mr. Douglass) than for me. 

 The strains and pressures within the machine may be very great, and 

 may require a corresponding strength of construction to cope with 

 them. Indeed this is the reason why the machine has been so often 

 taken asunder. Mr. Holmes seems to have spared no pains to render 

 his work secure, and no sign of weakness has, to my knowledge, 

 manifested itself during the late trials." 



* In 18G7 Mr. Ladd introduced the modification of dividing the armature into 

 two bcparatc coild, one of Nvhich fed the electro-magnets, while the other yielded 

 the induced currents. 



