PREFACE. 



The present volume is the third of a series in which 

 it is proposed to present, year by year, the principal dis- 

 coveries in the various branches of science, theoretical and 

 a}7plied the selection of subjects being made, primarily, 

 on the ground of their supposed importance, as marking 

 the stages of scientific advancement ; and, secondarily, as 

 being of interest to the general reader. A general sum- 

 mary of progress for the year in the different departments 

 precedes the volume, and is intended to give a connected 

 and systematic sketch of the more important announce- 

 ments, and usually contains much matter not presented in 

 the body of the work. 



It will, of course, be readily understood that, in the com- 

 pass of a single duodecimo volume, it is impossible to do 

 more than to touch very briefly upon what appear to be the 

 more noteworthy subjects. As far as the specialist is con- 

 cerned, he must necessarily have recourse, for full informa- 

 tion, to the Journals or Year-Books devoted to his partic- 

 ular department, of wliich scarcely any branch of science 

 is at present destitute. The aggregate of announcements of 

 original investigations and discoveries for any given year, 

 contained in these works, would alone fill many volumes. 



As no person, however learned, is competent to decide 

 upon the relative importance of facts and discoveries in 

 departments other than his own, the editor would be 

 far from arrogating to himself even an average ability 

 in this respect. He has, however, been so fortunate as 

 to secure the collaboration of some of the most emi- 

 nent men of science in this country ; and among those 

 to whom he has been indebted for communications of 

 original discoveries, abstracts of what has been done by 



