364 Notice of the pressure of the Atmosphere, fyc. 



(which method was commenced and recommended in this 

 Journal,) is uniformly pursued in this paper. It has also been 

 adopted in England. But the French, instead of diameter, 

 use thickness ; as it seems to us, with less propriety, for the 

 reasons given, vol. vi, p. 111. 



We regret to see the exploded error, of the axolotl's being 

 the larva of a water salamander, again put down as a matter 

 of undoubted science. It rests, indeed, here as elsewhere, 

 on the authority of Cuvier ; but even that authority cannot 

 support it against a simple examination of the specimens now 

 in the New- York Lyceum. The animal is, beyond all doubt, 

 mature and distinct from all others. 



Your cordial friend, 



D. H. BARNES. 



Art. XIV. — Notice of the pressure of the Atmosphere, fyc. 

 within the Cataract of Niagara^ in a Letter from Captain 

 Basil Hall, Royal Navy, f. r. s. 



to professor silliman. 



New York, Oct. 29, 1827. 



My Dear Sir : If you think the following notice of an ex- 

 periment which I made at Niagara, early in July last, wor- 

 thy of a place in your excellent Journal, it is much at your 

 service. 



You may remember, perhaps, that some time ago, it was 

 suggested by Messrs. Babbage and Herschell, in a paper, I 

 believe, upon barometrical measurements, that there was rea- 

 son to suspect a change of elastic pressure might be found in 

 the air near a water fall ; and it occurred to me, when I was 

 making preparation for the present journey, that a good op- 

 portunity, for bringing this subject to the test of experiment, 

 might present itself at the Falls of Niagara. I accordingly 

 provided myself with a mountain barometer, of great delicacy 

 of workmanship, in some degree differently fitted up from the 

 ordinary instruments of this description ; and it may be worth 

 while, to mention the particulars of its construction. 



In the first place, as it is essential to the accuracy of baro- 

 metrical measurements, that the tube be held in a vertical po- 

 sition, and as the instrument is often exposed, especially at the 

 upper stations, to the action of high winds, it is of con- 



