74 Scientific IrUeUigence. [Jan. 



constraction of a mill worked by the two powers (i. e. steam and 

 wind) ; and had not the present mode of navigation by the former 

 force been so widely diffused, it is more than probable that it 

 never would have occurred to me. 



I have the honour to be, Sir, your very obedient servant, 



J. M. Bartlett. 



XIV. Galvanic Experiment. 



(To Dr. Thomson.) 

 SIR, G/as^oio, Oct. 9, 1819, 



The other evening, when reclining on my pillow in a chamber 

 where on all sides darkness was distinctly visible, and while 

 rubbing my eyes, an employment by the by in which the hands 

 of the indolent are frequently engaged, I happened accidentally 

 to thrust my thumb below the superciliary ridge, at the same 

 time raising the upper eye-lid a little, and was somewhat asto- 

 nished to perceive a fine semicircle of light, which was perma- 

 nanent as long as I kept my thumb in the above position. To 

 ensure success, the room must be dark, and the nail of the thumb 

 must be towards the eye, and press considerably on the upper 

 eye-lid while in the act of raising it. 



This luminous appearance t ascribe to galvanic agency, but 

 probably it may be owing to some other cause. However, if the 

 experiment is actually new, and worthy of notice, you may insert 

 it in your magazine ; if not, you will pardon me for mentioning 

 such a trifle, and excuse the ignorance and presumption of 

 Your most obedient humble servant, 



W. R. 



*\jj,* Though the preceding fact is not new, I have inserted this 

 notice of it for the sake of many readers who may not be much 

 conversant with physiological investigations. — T. 



XV. Singular Substance found in a Coal Tar Apparatus. 

 By Mr. Garden. 



In one of the condensing vessels of an apparatus erected for 

 the distillation of coal tar, and for the purpose of exposing 

 various bodies to the action of that substance at a boiling heat, 

 there was found a considerable quantity of a concrete matter 

 which had distilled over with the volatile oil. The substance in 

 the state in which I received it was mingled with a portion of 

 darkly coloured tar oil, from which by repose it subsided in the 

 form of a granular-like crystalline mass ; when the oil was poured 

 ofi', and the remaining portion separated as much as possible by 

 passing the sohd matter between several folds of blotting paper, 

 it was digested in alcohol slightly heated ; in this way nearly the 

 whole was dissolved. ^ The solution upon cooling deposited an 

 abundance of crystals of a tabular shape, still coloured by a 

 small quantity of adhering oily matter ; by repeated solutions and 



