903 Transactions of the American Institute. 



plow over a large portion of the surface of the positive ball. If, in 

 this state, two or three small pieces of sealing-wax, or even a drop of 

 water, be placed on the negative pole, corresponding non-luminous 

 spots will appear on the positive pole, and these spots will rotate when 

 the negative pole is rotated. It is evident that lines of force pass 

 through the intervening air from the negative pole to the positive, 

 a distance of about eight inches. This experiment, Mr. Yarley 

 believes, may explain the cause of " ball lightning." If a cloud be 

 negatively electrified sufficiently strong to produce a flash from the 

 earth, a point on such cloud would correspond to the projection of 

 wood on the negative pole of the electric machine ; and such point 

 moving along the surface of the cloud would cause a responsive action 

 near the surface of the earth, and a luminous spot would appear, which 

 has been described as "ball lightning" by those who have witnessed 

 this rare phenomenon. 



Dr. L. Bradley — I think I have seen ball lightning. I saw it go 

 into a mill, and it was all in flames in an instant. It seems to be 

 totally unaccountable. 



Prof. P. H. Yan der "Weyde — I have once seen a ball of lightning. 

 This is the first explanation I have heard having any appearance of 

 truth. 



III. Mineral Cotton. 

 Mr. Coleman Sellers, of Philadelphia, exhibited, at a recent meeting 

 of the Franklin Institute, a sample of a product formed by allowing a 

 jet of steam to escape through a stream of liquid slag, by which the 

 sla<r is blown into the finest threads, sometimes two or three feet in 

 length. These threads of glass readily break up into much shorter 

 ones, which, being white, resemble cotton — hence the name. The 

 material is a slow conductor of heat, and as great quantities of air 

 must be retained in its interstices, it is well adapted to many purposes 

 where so-called non-conductors of heat are required. 



IY. Singular Action of Light upon Chlorine. 



Mr. E. Budde has described, in Pogg. Annalen, No. 10, 1871, a 

 series of experiments which show that chlorine gas expands much 

 more under the action of the violet rays than when exposed to the 

 red rays of the spectrum. The same result was obtained on substi- 

 tuting bromine for chlorine, thus revealing the new fact that some 

 bodies increase in volume under the actinic rays as others do under 

 the heating rays. He offers the following explanation of the phe- 



