PREFACE. 



In presenting to the public the fourth volume of the 

 series of the " Annual Record of Science and Industry," 



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some remarks may be fitly introduced in explanation of 

 the aim and scope of the work. 



In each of the successive numbers already published 

 new features have been introduced, suggested by experi- 

 ence as well as by the advice of the scientific collaborators 

 and friends of the editor. These are exemplified in part 

 by the increasing number of communications and criti- 

 cisms on progress in the various branches of science, and 

 by the greater extent of the historical resumes given under 

 the caption of " General Summary of Progress." These 

 have increased in the successive years from 16 pages for 

 1871, to 50 pages for 1872, and 114 pages for 1873. At 

 the same time, the volumes have successively increased in 

 the number of pages from 634 in 1871, to 651 in 1872, and 

 714 in 1873. 



The editor has been pleased to notice that his endeavors 

 thus to increase the value of the work have been on the 

 whole cordially appreciated by the public at large. With 

 much of praise, however, sundry friendly suggestions for 

 modifications and improvements have been made which 

 merit attention. It lias been urged, on the one hand, that 

 some discoveries and memoirs deserving of attention have 

 not been referred to ; on the other, that the preliminary 

 Summaries of Progress would be sufficient alone, without 

 any paragraphs recording individual discoveries. It would 

 of course be impossible to satisfy such discrepant opinions, 

 and in this dilemma the only resource left to the editor has 

 been to follow a mean which he hopes will be regarded by 

 most as a tolerably happy one. It must be remembered 



