10 REPORT OF THE SECRETARY. . 



tion to the literature of zoology, and will All a void in the descriptive 

 history of the mollusca of this country. One of its chief merits is that 

 in it are collected together from many sources notices of the labors of 

 all previous investigators, and in many cases extracts of all that is im- 

 portant from their works. How much the publication of such mono- 

 graphs has tended to the advancement and acceleration of our knowledge 

 of any group, the past history of zoology amply shows. 



Another article in this volume not previously described is that drawn 

 up by Professor Baird relative to inquiries as to the food-fishes of the 

 United States. It has been used by him in his capacity of United States 

 fish commissioner, but will be useful for reference to all who may be in- 

 terested in this subject. The questions relate to the names, distribution, 

 abundance, size, migration, relationship, food, reproduction, culture, 

 protection, disease, capture, and value of fishes. 



The circular on lightning-rods was prepared to save time in answering 

 the frequent inquiries as to the best means of protection from lightning. 

 On this subject it is proper to remark that the country is overrun with 

 patented inventions for alleged improvements in lightning conductors. 

 Most of these are founded on misconceptions of established principles of 

 electricity, and although they may in most cases, if properly connected 

 with the earth, serve to conduct a discharge which would otherwise be 

 attended by serious consequences, harmlessly to the ground, yet they do 

 not possess the character as to improvements which is claimed for them 

 by their vendors. 



The instructions for observations on thunder-storms originated in the 

 desire to obtain special information as to the origin, direction of move- 

 ment, and other facts relative to these interesting meteors, which are 

 intimately connected with tornadoes. The latter phenomenon occurs, 

 perhaps, more frequently in the United States than in any other country, 

 and from the devastatious which attend its progress over the surface of 

 the earth, it becomes an object worthy of attention of the public gener- 

 ally as well as the professed meteorologist. 



Another publication forming a portion of the Miscellaneous Collections 

 is the third and completing part of a series of monographs of the Diptera, 

 or two-winged insects, of North America, by Baron Osten Sacken, late 

 of the Russian legation, and Dr. H. Loew, of Prussia. The first part was 

 published in 1862, and included the families of Trypetidcc, Sciomyzidce, 

 EpJvydrinidw, and Cecidomyidcv. The second part appeared in 1806, and 

 consists principally of a monograph of iheDolichopodidcv. The fourth part 

 was issued in 1869, and embraces a monograph of part of the Tipulidw. 

 The third part, or that in question, includes the families of the Ortalidw 

 and Trypet'mcc. In variety of forms, says the author, the family of Orta- 

 lidw is scarcely surpassed by any other Diptera; at the same time it is 

 hardly equaled by any in the structural differences occurring among the 



