156 Obstructions to the Vibration of a Mercurial Pendulum, 



In 100 parts, alloy dissoved, 81-755, Iron, nickel and chlorine. 



riron, . . 9-940 

 *' " alloy separated, 18 -245 <! Nickel, . 7-465 



[pyrites, . -840 



The unequal distribution of the negative alloy throughout the 

 mass prevents the ultimate analyses of any two portions afford- 

 ing the same numbers ; and it is not certain that only one nega- 

 tive alloy exists. When a silver salt, especially the sulphate, is 

 used in the proximate analyses, some parts of the negative alloy 

 become firmly plated with silver, indicating a mixed composition 

 in the alloy. 



Your discovery of chlorides in this wanderer from unknown 

 regions is a fact of interest, not so much on account of its add- 

 ing more to the number of the constituents already known to 

 belong to meteorites, — its significance and importance in my 

 view are rendered more prominent, by their direct relation to a 

 state which a part of our earth might once have exhibited ; fa- 

 voring the conclusion that the chlorides and hydrochlorates of 

 our rocky strata may have resulted from the decomposition of 

 metalloidal chlorides existing with the metallic bodies from which 

 our rocks have been formed, the presence of our atmosphere 

 and moisture being sufiicient to destroy a state of repose and 

 carry it to the one of constant changes which we observe. 



With high regard, A. A. Hayes. 



Roxbury Laboratory, November 1, 1844. 



Art. XV. — Effect of a contracted space in obstructing the Vi- 

 brations of a Mercurial Pendulum ; by George Baker. 



While adjusting a mercurial pendulum, last autumn, which I 

 put to my regulator, I had occasion to observe closely the changes 

 in the arcs of vibration, which led to some investigation of the 

 cause. I found that during the last three days of the descent of 

 the weight, the vibrations were diminished 0° 6' on each side of 

 the point of rest, which I attributed to the near approximation of 

 the weight to the ball of the pendulum, causing an obstruction to 

 the displacement of the air by the motion of the pendulum, and 

 as I anticipated, caused the clock to lose during this portion of 

 the weight's descent, whereas during the other portion, when 



