Dr. Comstock's Grammar of Chemistry. 369 



below the Ohio, at only three and a half inches a mile, 

 which would produce, were there no resistance, a velocity 

 of only eighty-five hundredths of a mile an hour. He also 

 estimates the elevation of the source of the Mississippi* to 

 be less than that given by Mr. Schoolcraft; and, if the tide 

 water of the Hudson is lower than the waters of the Gulf 

 of Mexico, the descent of the Mississippi must be propor- 

 tionally diminished. It seems pretty evident that the al- 

 lowed velocity of the river is too great for the estimated 

 descent. It is certain, at least, that a more accurate de- 

 termination of the velocity of the current, as well as of the 

 elevation of the source of the Mississippi, is very desirable ; 

 and it is to be hoped that the remarks in Dr. Beck's Gazet- 

 teer will lead some of the western gentlemen to a satisfac- 

 tory result on one or both of these particulars. D. 



5. Dr. Comstock'' s Grammar of Chemistry. 



In the fifth volume of this Journal, the publication of this 

 work was mentioned. We by no means hold ourselves 

 responsible to give opinions of new works, but we owed the 

 respectable author of this manual, good-will enough to have 

 said a few words on the merits of his book, had it not been 

 postponed from mere inability to peruse it. 



If our opinion be of any consequence in this case, we are 

 gratified in saying that Dr. Comstock has executed his 

 work with very creditable ability and address. It is concise, 

 perspicuous and select, and bears strong internal evidence 

 of being the offspring, to a great extent, of a practical man, 

 who writes with the precision which can be derived from 

 experience alone. Those chemical compilations which are 

 made by men who have never performed what they describe, 

 resemble the fictitious travels of imaginary adventurers, who 

 delineate countries which they have not seen. In chemis- 

 try, the audivi may give a man many good ideas, useful to 

 himself; the vidi will still more enlarge his knowledge — » 

 but it is only the feci which qualifies him to instruct others* 

 Dr. Comstock's experiments are well chosen, well-describ- 

 ed, and made intelligible and practicable by wood cuts in^* 

 serted in the pages of the work.! — Ed. 



* Art. JVavigation Inland, in the New Ed. Encyc. 



("Perhaps it is a mark of his good, judgment and prudence that he has omit= 



Vol. VL— No. 2. 47 



