44 Dr BREWSTER on the Construction of Polyzonal Lenses 



reception I have experienced from that liberal and enlightened 

 body, has convinced me, that if I had made this application in the 

 year 1819, I should now have had the satisfaction of seeing the 

 new method of illumination introduced into our own lighthouses. 

 The Commissioners have allowed me opportunities of explaining 

 to them, both personally and in writing, the construction and 

 advantages of the new apparatus ; and I have been authorized 

 to have one of the Polyzonal Lenses constructed under my own 

 superintendence. This work has been entrusted to Messrs GIL- 

 BERT of London, who are now executing one of the lenses in 

 flint-glass, with a diameter and a focal length of three feet. I 

 have no doubt that the Trinity-House of London, and the Corpo- 

 ration for Improving the Port of Dublin, the two bodies who have 

 the superintendence of the English and Irish Lighthouses, will 

 also concur in putting the new method to the test of direct ex- 

 periment ; and I do not hesitate in expressing my conviction, 

 that, in a few years, it will be established in every maritime 

 country where the preservation of life and property has become 

 an object of public concern. 



Having thus given a brief account of the origin and history 

 of the new system of illumination, I shall now proceed to point 

 out its superiority to that which is at present in use. In doing 

 this, I shall adopt the following arrangement. 



I. On the imperfection of the present system of illumination 



by Hammered Reflectors. 

 II. On the construction and properties of the Polyzonal Lenses. 



III. On the combination of Lenses with Plain and Spherical 



Mirrors, for Fixed and Revolving Lights. 



IV. On the Construction of Distinguishing Lights. 



V. On the occasional exhibition of Powerful Lights in Light- 

 houses. 

 VI. On the introduction of Gas into Lighthouses. 



