1823.] Astronomical Society. 395 



siveness at 0°. Experiments had been made, with a view to the 

 liquefaction of oxygen, hydrogen, phosphuretted hydrogen, fluo- 

 silicic, and fluo-boracic gases, but these substances had hitherto 

 resisted all powers of condensation that the author had been able 

 to apply to them. With respect to the latter gas, this seemed 

 to arise from its great affinity for sulphuric acid, as discovered by 

 Dr. J. Davy, which is so great, that it even carries up that acid 

 with it, in the form of vapour. Mr. Faraday intimated, however, 

 that he should proceed with these experiments. 



GEOLOGICAL SOCIETY. 



April 4. — Two notices were read on a Recent Ligneous Petri- 

 faction. By the Rev. J. J. Conybeare, MGS. 



A notice was also read, respecting a Mass of Quartzose Fer- 

 ruoinous Sandstone, occurring in the Limestone near Bristol. 

 By George Cumberland, Esq. Hon. MGS. 



April 18. — A letter was read, containing " A Description of 

 Two New Species of Encrinus found in the Mountain Lime- 

 stone near Bristol." By the same. 



A letter was also read, " On the Geology of Pulo Nias, an 

 Island on the Western Side of Sumatra.*' By Dr. Jack. (Com- 

 municated by H. T. Colebrooke, Esq. MGS.) 



A paper was read, " On the Geology and Geography of 

 Sumatra, and some of the adjacent Islands." By Dr. Jack. 

 (Communicated by H. T. Colebrooke, Esq. MGS.) 



ASTRONOMICAL SOCIETY. 



April 11. — A letter was read from M. Pastorff to the late 

 President, on a Photosphere observed at Buckholts, in Germany, 

 round Venus, Jupiter, and Saturn. 



At the same meeting was read, an Extract of a Letter from 

 M. Littrow, Director of the Imperial Observatory at Vienna, to 

 the Foreign Secretary, relative to the Cause of certain Discre- 

 pancies in Astronomical Observations ; on the Construction of 

 Instruments, and on Correction for Refraction. 



Article XVI. 



SCIENTIFIC INTELLIGENCE, AND NOTICES OF SUBJECTS, 

 CONNECTED WITH SCIENCE. ' 



I. Alkanet as a Test. 

 Dr. Robert Hare, of Philadelphia, finds that the colour of alkanet 

 may be used instead of litmus, producing the same phenomena, but in 

 a reversed order; for the alkanet infusion is made blue by an alkali, 

 and restored by an acid, instead of being, as in the case of litmus, red- 

 dened by an acid, and restored by an alkali. Thus as the one is indi- 



