236 Choak and Fire Damp in Mines. — Electricihj. 



ftt.i!, and ahvsys follows the same laws : the formula' of M. La-* 



place therefore apply to them always. 



" Some previous infjuiiics had already led me to recognise a 

 singular opposition in the natui-e of the impression which various 

 crystals give to light in polarizing it. I had expressed this 

 opposition by the terms quarlzous polarizalion and htriUatcd 

 pdlarizaliov, Trom the substances which had first exhibited this 

 opposition. I have now ascertained that all the crystals en- 

 dowed with the quartzous polarizatimi arc attractive, and all 

 those which exercise the berillated j)olari:<ation are repuLive. 

 Iceland spar belongs to the latter class, 



" These results show that there exists in the action of crystals 

 upon light, the same opi)ositi(m of forces which has been already 

 recognised in several other natural actions, such as the two kinds 

 of magnetism, and the two kinds of electricity. To this also the 

 other ol)servations lead, which I have already published on the 

 oscillations and rotations of luminous particles." 



CHOAK AND FIRE DAMP IN MINES. 



Dr. Watt, of Glasgow, informs us that a Mr. Davidson, \\}m 

 has been blind from childhood, is now delivering lectures in Scot- 

 land, on natural philosophy and chemistry. The circumstances 

 in which he is placed have led him to adopt, in many cases, far 

 more sensible modes of experimenting, and easier plans of ef- 

 fecting his ))urposes, than are commonly employed by lecturers. 

 But we chiefly mention the eiroumstance, in the hope that it may 

 be the means of bringing Mr. Davidson acquainted witli the So- 

 ciety in Sunderland for preventing Accidents in Coal Mines ; 

 as. Dr. Watt informs us, that among other contrivances he has 

 invented a mode of clearing mines from deleterious gases, which 

 for efficacy, facility, and cheapness, is preferable to any of thii 

 methods hitherto employed. 



ELECTRICITY, / 



Monsieur de Nelis, an indefatigable inquirer into the pha^no-: 

 mena of electricity on the continent, having favoured the Edi- 

 tor of the Philosophical Magazine with several valuable com- 

 munications, accompanied by various specimens of electrical 

 results ; Mr. Singer, the eminent lecturer in electricity and 

 Galvanism, has kindly undertaken to repeat the experiments of 

 M. Nelis, and to lay an account of them before the readers of 

 the Philosophical Magazine. In the mean time it may not be 

 amiss to state generally, that M. de Nelis has directed his atten- 

 tion to the subject of electricity for upwards of fifteen years ; 

 and he conceives that all his experiments demonstrate t!i,e 

 leading principle of Franklin's theory;, namely, the existence pf 

 ' a single 



