414 Miicellaneous Jntelligefiee. 



13. Alum in decomposed Mica Slate. — Among the sources of 

 alum there is one which we have never seen mentioned by any 

 author. It is from the decomposition (not of clay-slate, but) of 

 mica-slate. We have been frequently presented with specimens 

 of alum found in decomposed mica slates, as from the towns 

 of Preston, Waterbury, and Huntington in Connecticut, and 

 indeed we have seen but few instances of American alum de- 

 rived from any other source. It is, as we are informed, so 

 abundant in some places, that the people use it in dyeing without 

 resorting to any other supply. We are not aware that this 

 source of alum has been observed in other countries. — American. 

 Journal, iii., p. 240. 



14. American Hydraulic Lime. — The following is an analysis 

 made of an excellent hydraulic lime used in the construction 

 of the great canal in the state of New York : 



Carbonic acid . . 35.05 



98.2 



It will not slake, but is pulverized, and then mixed with 

 half its quantity (probably bulk) of sand. 



§ II. Electricity, Magnetism, &c. 



1. Effects oj" Lightning. —A house at Geneva, which had plates 

 of tinned iron disposed in various ways about the roof and 

 other parts, was struck by lightning on the 3d of July. The 

 lightning produced various effects here and there, but among 

 them none was more remarkable than that produced on 

 one of the plates of tin that had been placed on the roof 

 against the chimney. This plate is pierced with two circular 

 holes, about an inch in diameter each, and four inches apart. 

 Each hole is strongly burred, but the remarkable circumstance 

 is, that the burs of the two holes are in opposite directions, 

 which, according to M. Pictet, either indicates that the electric 

 fluid has passed through the plate forming one hole, has moved 

 five inches along it, and then gone through again ; or that- 

 there were two currents of fluid which moved simultaneously 

 in opposite directions, at five inches distance from each other, 



2. Production of Magnetism. — M. Poenitz of Dresden has 

 lately experimented on the production of magnetism by ham- 

 mering, friction, &c., and has come to the conclusion, per- 



