much more volatile than silver, and states an experiment made with 

 mercury in the winter of 1824-25, where no action on gold-leaf, 

 suspended over it, however near, took place, from which he con- 

 cludes the mercury then to have been perfectly fixed ; and other ex- 

 periments on mercury and on sulphuric acid by Sir H. Davy and 

 Signer Bellani are adduced in support of the same view. 



But there is another force, that of homogeneous attraction, which 

 the author regards as sufficient to overcome a certain degree of vapo- 

 rous elasticity ; and he illustrates the mode of action of this force by 

 an experiment on the slow crystallization of camphor, and by that of 

 other substances from vapour in the process of sublimation ; and by 

 analogous phenomena in the crystallization of salts from aqueous 

 solutions. 



On Electrical and Magnetic Rotations. By Charles Babbage, Esq. 

 F.R.S. SfC. 8(C. Communicated May 29, 1826. Read June 15, 1826. 

 iY. Trans. 1826, p. 494.] 



The author first recapitulates the manner in which he conceives 

 time to influence the results of the magnetic phenomena observed by 

 M. Arago, and which need not here be -repeated, being in substance 

 that given in a paper on the subject, in the Transactions of last year, 

 stated in a more geometrical form. As the reasoning in this argu- 

 ment requires only that an attractive or repulsive force should be 

 communicated from one body to another in a finite time, it occurred 

 to him that electricity might be substituted for magnetism, and that 

 rotations analogous to those observed by M. Arago might be pro- 

 duced by the use of electrified instead of magnetic bodies. He 

 accordingly suspended by a fine silk thread a thin brass bar with 

 circular ends over a disc of glass ; and the bar being electrified by 

 contact with excited sealing-wax, the glass was made to revolve 

 slowly, when the bar was observed to be dragged round in the same 

 direction. The effect was decided ; and all proper precautions were 

 taken to avoid disturbing causes, such as currents of air, twist of the 

 silk, &c. The effect was greatest with a slow velocity of rotation, 

 about five turns in a minute. On substituting a stick of excited 

 sealing-wax for the brass bar, the same effect was produced ; but 

 when the rotation of the plate was rapid, the stick remained nearly 

 immoveable. The same effect was produced when the glass plate 

 was covered with plates of copper, lead, or other metals cemented 

 to it. 



A proper apparatus being constructed for the purpose of further 

 experiments, an excited electrophorus was made to revolve under a 

 flat needle of thin brass with circular ends, with various degrees of 

 rapidity. The motions of the needles were irregular and complicated, 

 but appear to the author capable of explanation, as well as the others 

 on the same principle, that electricity excited by induction is not in- 

 stantly destroyed by removing the inducing body. 



