VOL. I.] PHILOSOPIUCAL TRANSACTIONS.' 35 



weigh above a hundred weight, and is easily put in all sorts of positions. The 

 focus is distant from the centre of the glass about three feet, and is about the 

 size of half a louis d'or. One may pass one's hand through it, if it be done 

 nimbly; but if it remain there for one second only, there is danger of receiving 

 much hurt. 



Green wood takes fire in it in an instant, as do also many other bodies. 



Seconds. 

 A small piece of pot-iron was melted, and ready to drop do\vn, in ... . 40 



A silver piece of 1 5 pence was pierced in 24 



A thick nail (called le clou de paisan) was melted in 30 



The end of a sword-blade of olinde was burnt in 43 



A brass counter was pierced in Q 



A piece of red copper was melted, ready to drop down in 42 



A piece of a chamber quarry-stone was vitrified in 45 



Watch spring steel melted in '. 9 



A mineral stone, such as is used in harquebusses d. rouet, was calcined 



and vitrified in 1 just, 



A piece of mortar was vitrified in 52 



In short, there is hardly any body which is not destroyed by this fire. To 

 melt by it any great quantity of metal much time would be required, the action 

 of burning not being performed but within the size of the focus ; so that usually 

 only small pieces are exposed to it. M. d'Alibert bought it for 1500 livres. 



This information has caused the following further particulars to be com- 

 municated from Paris: — 



I see by some letters that you incline to believe that the glasses of Maginus 

 and Septalius approach to that of Lyons. But I can assure you they come very 

 far short of it. You may consult Maginus's book, where he describes his ; and 

 there are some persons here who have seen one of his best, which had but 

 about twenty inches diameter : so that this of Lyons must perform at least twice 

 as much. As to Septalius, we expect the account of it from intelligent and im- 

 partial men. It cannot well be compared to that of Lyons, unless in bigness ; 

 and in this case, if it have five palms, as you say, that would be about 3^- feet 

 French ; so that would be again a foot larger in diameter, which would make it 

 as much again greater in surface. But its effects, as it bums so far ofF, cannot 

 be very violent. And I have heard one say, who had seen it, that it did not set 

 wood on fire but after the time of saying a miserere. You may judge of the 

 difference of the effects, since that of Lyons gathers its beams together within 

 the space of seven or eight lines ; and that of Septalius must scatter them in the 

 compass of three inches. 



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