NATURAL PHILOSOPHY. 109 



of powerful magnets and iron cores with surrounding coils, accurately 

 arranged, so that when the associated cores were revolving they sent 



^3 ' < ' 



all their currents into one common channel, from whence they were 

 conveyed to the lantern by conducting wires, and there produced the 

 electric light. There was no consumption of material or energy, 

 other than that of the burning fuel required at the steam engines to 

 produce motion. 



A trial of the light began in the lighthouse on the 8th of Decem- 

 ber, 1858; but as the apparatus was imperfect in some points, and 

 the results unsatisfactory, the lighting by the apparatus was suspended 

 for a while, that the defects might be remedied. The lighting was 

 renewed in March, 1859, and during the following month it was care- 

 fully examined by Prof. Faraday. In his subsequent report to the 

 Trinity Board, ai'cer describing very fully the observations he made 

 at sea, and the various experiments by which he tested the power of 

 the light, he states his opinion that Prof. Holmes had practically 

 established the fitness and sufficiency of the magneto-electric light for 

 lighthouse purposes, so far as its nature and management are con- 

 cerned ; that the light produced was powerful beyond any other that 

 he had seen so applied, that its regularity in the lantern was great, and 

 its management easy. Ten months after he had thus expressed his 

 approval of the experiment, he again visited the light, and found it 

 of the same character as when he had last seen it. It was generally 

 very steady, but with slight interruptions now and then from iron in 

 the carbons. He found that it had a tendency to sudden and spon- 

 taneous extinction, arising either from the breaking off of the end of 

 the carbon, or from some disarrangement in the fine mechanical work 

 of the lamp. This happened three or four times every night ; and 

 being once extinguished the lamp did not relight of itself. The 

 slightest touch of the keeper's hand, however, was enough to restore 

 the light ; but the liability to temporary extinction occasioned an 

 anxious watchfulness on the part of the attendant, who was con- 

 strained on this account to stay in the lantern continually. The 

 light had never been stopped by any deficiency of action in the 

 machine-room. 



The appointed time during which the magneto-electric light was to 

 be placed under practical trial at the South Foreland having, 

 early in 1860, come to an end, Prof. Faraday urged the Trinity 

 House to authorize its application, either there or somewhere else, 

 for a further and a longer period, stating that it had proved to be 

 practical and manageable, and had supplied the means of putting into 

 a lighthouse lantern, for six months or more, a source of illumination 

 far surpassing in intensity and eiiect any other previously employed. 

 Acting on this suggestion, the Trinity Board established an electric 

 light at Dungeness. At this lighthouse it is placed in an optic appa- 

 ratus constructed especially for it, which is only sixteen inches in 

 height, and fourteen inches in external diameter. The apparatus con- 

 sists of six lenticular zones and seven reflecting zones ; of the latter 

 three are below and four above. At the South Foreland there was 

 one electric lamp placed in the centre of a Fresnel optic apparatus. 

 Here there are two of the new optic apparatus, placed one over the 

 other in the axis of the lantern, and four electric lamps: for 

 10 



