If^ IMPROVED METHOD OF CONSTRUCTING SHIPS. 



That the pupil contra6ls as the quantity of light which falls 

 upon the eye increafes, is well known. 



And that the magnitude of the pi6ture of a luminous object 

 upon the retina, decreafes as the pupil contrads, is evident 

 from the experiments. 



Therefore, the magnitude of the picture upon the retina, 

 decreafes, as the quantity of light falling upon the eye in- 

 creafes. 



Hence the apparent magnitude of the moon is greateft at the 

 horizon, and decreafes as (he afcends ; for the magnitude of 

 her picture upon the retina is inverfely as the quantity of light 

 which (he gives us. 

 ^d to the fun. The fun appears larger at the horizon than at higher altitudes, 

 for the fame reafon ; and terreftrial objeds feen through a mift 

 appear larger than in a clear day_, in confcquence of the famq 

 operation of the eye. 



I am. Dear Sir, 



With much refpefl. 



Your humble Servant, 



E. WALKER. 

 lynn, Oa. 13, 1804. 



VI. 



Dejbription of the Ship Economy^ 200 Tons Meafurement, built 

 on the improved ConjlruSiion of Mi\ J. W. Bos well. ^ 



-a- HE plan adopted in the formation of this (hip is that defign- 

 ed for large (hips of 500 tons and upwards, and the third men- 

 tioned in my fpecification f. 



Its external appearance is nearly the fame as that of any other 



veflel of the fize, and the outward planking done in the ulbal 



Tnanner. Jt»is the internal conftrudion alone to which the patent 



relates, and that is as follows ; 



Dcfcription of a The beft general idea of it will be obtained by conceiying a 



vefftl framed in ^gfl-^j j^^jif with timbers, or ribs, much fmaller than ufuai, with 



a new method. 



♦ For which he has a patent. 



•f- See Vol.11. Second Series, p. 31, of Repertory of Arts. 



an 



