X. LIGHTHOUSES, ETC. 545 



currents are, cceteris paribus, more favourable regulators than those in a con- 

 stant direction. The machines of the Compagnie PAlliance had originally 

 six discs ; these were reduced to four when the improvements introduced into 

 the coils and the magnets permitted of a greater intensity being obtained with 

 these smaller machines than with the former. In the case of lighthouses, 

 where there cannot be too great intensity, the number of six discs has been 

 preserved. 



The central depot in Paris has retained, since 1860, the first specimen con- 

 structed by M. Van Malderen of this machine, with the currents not brought 

 into one constant direction. It has six discs, and carries 56 magnets ; it is 

 1-63 metre high, and 1-43 metre in diameter; it gives less light than the 

 present machines, but it works very well still, and serves for the experiments 

 that are made at the depot. 



This first machine of the Compagnie 1' Alliance may be regarded as the 

 starting point of all the attempts which have since been made of economically 

 transforming power into electricity, and consequently into light. On that 

 account it is no more than right, although the machine is not included iu the 

 Exhibition, to make mention of it in the catalogue. 



22O3. The Original Model of the Eddystone Light- 

 house. 



The Eddystone Rocks, so named from the great variety of sets 

 of tides and currents which surround them, are situated about 14 

 miles S.S.W. of the port of Plymouth, the sea being fully 

 30 fathoms in depth. A lighthouse was constructed on these 

 rocks by Winstanley in 1696, and destroyed by a storm in 1703. 

 A second was built by Rudyerd in 1709, and was totally consumed 

 by lire in 1755. The present lighthouse was commenced in 1756, 

 and completed in 1759, by Smeaton, F.R.S., civil engineer. This 

 original model, made by Smeaton, was sent by royal command for 

 the inspection of His Majesty George III. and the Royal Family, 

 and has since then remained in the possession of Mr. Smeaton's 

 family. Mrs. Croft Brooke. 



2203a. Model of the Lighthouse on La Corbiere Hock, 

 Jersey. Sir John Coode. 



The first lighthouse constructed in concrete ; tower erected in 1874. Sir 

 John Coode, engineer. Modelled by Mr. Joseph Thomas. Scale, y of 

 natural size. 



22O3b. Parabolic Reflector, rendered .holophotal, accord- 

 ing to Mr. Thomas Stevenson's design, by being fitted with a lens 

 and reflecting prisms, and a portion of a spherical mirror, so as to 

 parallelise all the light of the lamp. Introduced in 1849. 



The Commissioners of Northern Lighthouses. 



When the apparatus is to be cleaned the lamp is lowered out of the 

 reflector on a sliding carriage, as arranged by the late Mr. Robert Stevenson, 

 in 1814. The object of the sliding carriage is to insure the return of the 

 burner to the proper focus. 



40075. Mm 



