64 Proceedings of Philosophical Societies, [July, 



house ; this changed the period of the maximum effect from, 

 eleven o'clock in the morning till four in the afternoon ; but the 

 discrepancy continued, and consequently remains unaccounted 

 for. 1 he same difference of variation in the two situations was 

 also found by Mr. Christie, whose house is at some distance 

 from Mr. Barlow's, and who, at the suggestion and request of 

 Mr. B. carried on a similar but totally distinct series of observa- 

 tions, and was led to the same results without being aware 

 that they had occurred to Mr. Barlow. 



The following paper was also read : On Bitumen in Stones ; 

 by the Right Hon. George Knox, FRS. 



The results of Mr. Knox's experiments on the pitchstones of 

 Newry and Meissen, already before the Society (Phil. Trans. 

 1822, p. 313; Annals, N. S. iv. p. 460), had induced him to 

 submit a great number of other minerals to similar trials. Among 

 these, the following yielded various proportions of bitumen and 

 water : Pitchstone, from the Isle of Arran lost 4*705 per cent, by 

 distillation, about 3 of which were bitumen, and the residuum, 

 as in many other cases, was pumice ; pearlstone from Tokay, in 

 Hungary ; obsidian yielded much bitumen, as did the basaltic 

 greenstone, which forms a vein in the granite of Newry, parallel 

 to that of pitchstone ; basalt from Disko Island, and from the 

 Giant's Causeway ; ivacke from Disko Island yielded 1 1 per cent, 

 of bitumen ; iron clay from Howth ; bole from Disko Island ; me- 

 nilite from Menil-montant; adhesive slate from the same place ; 

 common serpentine from Zo'eblitz in Saxony ; mica slate yielded a 

 small quantity of bituminous water ; clayslate from Bangor ; 

 fetid quartz from Nantes gave 2 per cent, of bituminous water ; 

 felspar from Aberdeen, a little. 



The following substances sustained no loss of weight by distil^ 

 lation : pumice from Lipari fused ; rock crystal underwent no 

 alteration ; a colourless crystal of adularia, 



Mr. Knox states, as the general result of his researches, that 

 nearly all the minerals belonging to Werner's floetz-trap forma- 

 tion, contain bitumen ; and that it likewise exists, but in smaller 

 quantity, and more difficultly separable, in some of the substances 

 which constitute the older rocks. 



The paper concluded with some remarks on the new precau- 

 tions in the analysis of stones, which the author's experiments 

 just noticed seem to indicate the necessity of ; since it would 

 appear that the loss of weight by ignition, generally estimated as 

 water, may, in reality, be partly owing to the expulsion of 

 bitumen. 



June 19. — As this was the last meeting of the Society for the 

 present session, little more than the titles of the following papers 

 could be read : 



On Astronomical Refraction ; by J. Ivory, Esq. FRS. 

 Tables of certain Deviations which appear to have tfiken 



