XCVI. NEW SOUTH WALES LIGHTHOUSES. 



ments made on silver plate of the kind used in lighthouse 

 apparatus, it was found that at 45° incidence only -556 of the 

 incident light was reflected, and from experiments made with a 

 reflecting prism of glass, it was found that the amount of light 

 transmitted was *806 of the whole, which shews that by using 

 glass a saving of one-fourth is effected, and establishes the 

 superiority of glass over metal for lighthouse purposes " 



The catoptric mirror is formed by the revolution of a parabola 

 about its axis, and if a light be placed in the focus of the para- 

 boloid so generated, all the incident rays will be reflected in a 

 direction parallel to the axis from the w r ell known property of the 

 parabola, that if from a point on the curve lines be drawn to the 

 focus and parallel to the axis, these lines will make equal angles 

 with the tangent at the same point. 



The dioptric system was invented by Augustus Fresnel in 

 France in 1822, and the first light on this principle was that of 

 Cordouan at the mouth of the Garonne. It was introduced into 

 England in 1835 by Mr. Alan Stevenson. 



In 1845 M. Leonor Fresnel reported to the American 

 authorities that lights fitted with dioptric apparatus were incon- 

 testably superior to those fitted with catoptric apparatus, that if 

 we take into account the first cost and maintenance we find in 

 respect of the effect produced, the new system is from one and a 

 half to twice as advantageous as the old, and in 1852 the 

 American Board resolved that the Fresnel — or lens system modi- 

 fied in special cases by the holophotal apparatus of Mr. Thos. 

 Stevenson — be adopted as the illuminating apparatus of the 

 United States to embrace all new lights now or hereafter 

 authorised, and all lights requiring to be renovated by reason of 

 deficient power or defective apparatus. 



Description of New South Wales Lighthouses. 



There are twenty coast lighthouses, twelve of the larger class 

 of harbour lights, and two lightships. Six of the coast lights are 

 of the first order dioptric, viz.: — Green Cape, Montagu Island, 

 Macquarie (South Head), Sugar Loaf (Seal Rocks), Smoky Cape 



