REPORT OF THE SECRETARY. 11 



of the fresh-water algse except the diatomaceoa, which are so numerous 

 as to constitute in themselves a special object of study. 



The synonoiny of Professor Eabenhorst has been generally followed, 

 this naturalist having gone over the subject most thoroughly, with full 

 access to all its literature. " To attempt to differ from him," says Dr. 

 Wood, "would cause endless confusion. I have therefore nearly always 

 contented myself with his dictum, and have referred to him as authority 

 for the names adopted." The memoir in question consists of 272 pages, 

 and is illustrated by 21 quarto-plates of a very expensive character, since 

 they required in most cases a number of priu tings to produce the differ- 

 ent colors. 



Another investigation to the prosecution of which the Institution has 

 contributed is that by Mr. William Ferrel relative to the tides. To this 

 subject the author has given much attention, and has completed a me- 

 moir in regard to it, which is now in the press. This memoir does not 

 purport to be a regular treatise on the tidal theory, but is for the most 

 part supplementary to what has already been done. It does not, there- 

 fore, include elementary principles, but pertains principally to those parts 

 of the general theory iu which new results are attainable or old ones 

 susceptible of being presented in a more concise and simple manner. 

 For the author's purpose, however, it was necessary to go over much of 

 the ground which had been investigated; but all those parts of the sub- 

 ject which had already been well treated are passed over with a mere 

 reference as to where they might be found. At the time when this subject 

 was treated by La Place, Young, and Airy, but few observations had 

 been made and little attention had been given to the accurate compari- 

 son of the results of observation with those of theory, or to the forma- 

 tion of tables for the purpose of predicting the time of the phases of the 

 tides. For accomplishing the result it is necessary to obtain not only 

 an accurate development of the solar and lunar disturbing forces, but 

 also to determine the expressions which shall represent most accurately 

 the tidal relations to any one part of the whole of these disturbing forces. 

 "Every investigator of the tides," says the author, "must frequently have 

 felt the great need of formulae of this kind prepared to his hand, which 

 he could use and thus save the labor of difficult developments and ac- 

 curate determinations of co-efficients in special cases." This great need 

 the author has attempted to supply. 



Believing that most of the hitherto unexplained apparent anomalies 

 in the tides are due to the friction of the water on the surface of the 

 earth, the author has given special attention to the effects of this in 

 all the various cases, not only on the hypothesis of its being in direct 

 proportion to the velocity but also as the square of the velocity. The 

 results obtained in this part of the investigation are regarded as being 

 interesting and important in relation to some of the phenomena of the 

 tides which have not hitherto been explained, especially to the occurrence 



