Dr Wollner on the different Forms of Salts , $c. 289 



ed to communicate motion to the pendulum in smaller arcs of 

 vibration, and found the beats of the clock to be suspended in 

 times proportionally less ; so that, in the last experiment, the 

 beating of the clock was stopped in the short space of fifty-nine 

 seconds. 



On examining the spill or index, to the reciprocal influence 

 of which and the horse-shoe magnet I attributed the pheno- 

 menon, I found it to display the most decided marks of pola- 

 rity. A small pocket compass, placed below its extremity, had 

 the direction of its needle completely inverted at every oscilla- 

 tion of the pendulum. The south pole being attracted by it 

 when quiescent, indicated the kind of polarity it possessed, and 

 which might have been anticipated from the necessary position 

 of the pendulum. 

 Plymouth, 



February 17, 1827. 



Art. XXVI. — On the different Primitive Forms of the same 

 Salt produced by a Change in the Nature of the Solvent.* 

 By Dr Christian Wollner. With Observations by the 

 Editor. 

 In the manufactory of alum at Putchen, near Bonn, Dr 

 Wollner had occasion to observe, that in the tubs which con- 

 tained the mother waters there were formed crystals of sul- 

 phate of iron, which had exactly the same form as alum, that 

 is, which had the form of the regular octohedron. Having 

 analysed these crystals, he found them to be composed, like 

 the common copperas, as follows : 



He made several attempts to obtain similar crystals from a 



* Kastner's Archiv. fur die gesarnmte Naturlshre, torn. vi. p. 364-, or 

 Ferrussac's Bull, des Sc. Nat. Dec. 1826, p. 392. 



VOL. VI. NO. II. APRIL 1827- T 



