iv PREFACE BY THE EDITOR. 



which they give to physical science. Here will be found, for the first 

 time, correct notions on capillary action. Here Dr. Young developed 

 the beautiful principle of interference, " that fine discovery," to use the 

 words of M. Arago, " which will render his name imperishable." 



What Dr. Young has done cannot, however, be better explained 

 than in 'his own Preface, of which it is sufficient to remark, that the 

 Author has in no instance over-estimated the importance of his labours. 



It only remains to add a few words relative to the present edition. 

 In some of the subjects treated of, considerable advances have been 

 made since the Lectures were first published. To render the work as 

 complete as possible, the Editor has supplied brief expositions of what- 

 ever additional discoveries have been made, which are printed along 

 with the Lecture on that branch to which they belong, and distin- 

 guished by being inclosed within brackets. They serve, for the most 

 part, to complete the subject according to the plan of the Author. In 

 the case of Electricity, and its kindred branches, so much addition 

 has been made within the last half-century, that it would greatly 

 exceed the necessary limits to treat of those sciences satisfactorily. 

 All that has been attempted is to offer a very brief sketch of the 

 nature of the extension of those sciences, without entering at all into 

 details. 



The authors to whom Dr. Young directly refers in the Lectures are 

 given at the foot of the page, the name and date of the work being 

 added, and in many cases the page which is referred to. Accompany- 

 ing these references will be found others to authors who have treated 

 on the same subject. At the end of each Lecture is given a table of 

 additional authorities, a portion of which have been extracted from Dr. 

 Young's own catalogue. Indeed these tables embrace every important 

 work which the catalogue contains, and, except in Meteorology and 

 Astronomy, reference to all the most valuable memoirs found in the 

 different scientific transactions. In the excepted cases, the lists were 

 too extensive, and too little suited to the character of this work to be 

 given entire, whilst abridgement would have answered no useful purpose. 

 With respect to the additions which the Editor has made to this branch, 

 they will be found to be very extensive ; and it is believed the whole 

 forms a tolerably complete body of scientific literature. There must 

 necessarily be expected some important omissions, but it is hoped they 

 are not numerous. For the guidance of those who shall consult these 

 catalogues, it is necessary to point out the fact, that condensation has 



