PREFACE. 



Every person that uses the Microscope for anything except some 

 one special purpose, will probably, at some time or other, be inter- 

 ested in diatoms, from the simple fact that they meet us almost 

 everywhere, and present attractions and beauties which, when once 

 seen, are pretty certain to rivet the attention of the observer. As 

 test objects they have occupied very largely the attention of those 

 who have studied the improvement of the microscope, and that they 

 have exerted a powerful influence in bringing our objectives up to 

 their present high standard, cannot be denied. Unfortunately their 

 life-history has not been so generally studied, because perhaps 

 microscopists have contented themselves with the use of objects 

 obtained ready mounted from the dealers, instead of collecting, pre- 

 paring and mounting them themselves. 



It is to aid them in this that we have brought together the 

 following tracts, which give the latest and best information on the 

 subject. The paper by Dr. Edwards formed a portion of the 

 "Natural History of the State of New Hampshire," of which but a 

 very limited edition was issued. A small portion of the present 

 paper (that devoted to collecting) was printed separately, and 

 pretty widely distributed, but the directions for preparing and 

 mounting have only been accessible in a somewhat expensive form. 

 The papers by Prof. Johnston and Prof. Smith appeared in the 

 "Lens, "and are not now procurable, except at considerable cost. 

 We have therefore thought that it would be doing a good service to 

 the cause of microscopy to reproduce these three papers. To the 

 authors we owe our best thanks for thtir Liberal permission to 

 reproduce tin m. 



THE PUBLISHERa 



