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 tne Journal, the publication of io 
work was mentionéd. y 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 1s 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 
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 fect 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 i in the pages of the work. |—Ed. 
* Art. Navigation Inland, in the New Ed. Encyc. 
tPerhaps it is a mark of his good judgment and prudence that he has omit- 
Vor. VI.—No. 2. 47 
