70 Mr. Barnes on Magnetic Polarity. 



tufts of the branchiae ; but by others this is doubted. • Capt. 

 Le Conte has dissected a large Siren alive, and has actually 

 seen the expansion and contraction of the lungs in the act of 

 respiration, just as in the frogs and tortoises ; and he has also 

 made a beautiful preparation of the lungs, by inflating them 

 with air and drying them in that state. They are true lungs 

 and not merely air-sacks, and their connexion with the heart 

 and arteries was distinctly observed. This is an important 

 fact, and it will be duly appreciated, and placed to the credit 

 of that very accurate observer, to whom, in various ways, 

 natural science is already so much indebted. It is hoped that 

 the learned Professor of the University of Vermont who dis- 

 sected the Proteus Maculatus, as mentioned above, will, by 

 the dissection of a number of living specimens, finally settle 

 this long contested and doubtful question. He has, what 

 very few other competent persons can have, the means at 

 hand, and we hope that zeal and industry will not be wanting. 



Your cordial friend, 



D. H. Barnes. 



Art. X. — Notice respecting Magnetic Polarity ; by D. H. 



Barnes. 



to professor silliman. 



New -York, April 16, 1827. 



Dear Sir, — Professor Eaton's demonstration, of the fact, 

 that the fitful variation of the compass is caused by the mag- 

 netism of the card, gave us great pleasure, and the simple 

 and efficient remedy which he has found, is no less honorable 

 to himself than beneficial to the community. Mr. Patten, 

 of this city, had discovered the same fact in a compass 

 which he had proscribed as unsalable, and laid by as useless. 

 Trying this compass with its proper needle, we observed 

 that in turning the compass slowly and steadily around, 

 there was one point to which the needle would cling, until 

 the compass was turned full ten degrees. The needle would 

 then start off, suddenly, to the proper point, and traverse cor- 

 rectly until again interrupted by the point of attraction in the 

 rim. The same compass was then tried with a short needle 

 which lay perfectly still, and pointed with the utmost exact- 

 ness, while the compass was turned entirely round. While 



