OP ARTS AND SCIENCES. 349 



Edwin H. Hall presented by title a paper On the Thermal 

 Conductivity of Mild Steel. 



Henry Taber announced that he had proved the" sufficiency 

 of certain conditions that in Volume XL VI., page 583, of the 

 Mathematische Annalen, he had shown to be necessary in order 

 that a transformation of the group whose invariant is a cer- 

 tain linear complex may be generated by the repetition of an 

 infinitesimal transformation of the group. 



Eight hundred and eightieth Meeting. 



February 12, 1896. — Adjourned Stated Meeting. 



The President in the chair. 



The chair announced the death of Martin Brimmer and 

 Richard Manning Hodges, Resident Fellows. 



The Corresponding Secretary read a letter from Augustus 

 St. Gaudens, acknowledging his election as Associate Fellow. 



The President reported that no change of quarters for the 

 Academy was feasible at present. 



George L. Goodale read a paper on Forestry under New 

 England Conditions. 



John Trowbridge gave an informal account of his experi- 

 ments with the cathode rays. 



No evidence of refraction was detected. Wooden lenses, 

 both double convex and double concave, were tried, and 

 apparently did not affect the rays. In Helmholtz's discussion 

 of the electro-magnetic theory of light, there is a longitudinal 

 wave which travels with an infinite velocity. Such a wave, 

 travelling faster than the velocity of light, would not suffer 

 refraction. The photographs procured by the new rays are 

 not strictly shadow pictures, such as may have been obtained 

 before in the electro-static field. They show a specific ab- 

 sorption which is a new phenomenon. For instance, a disk 

 of microscopic cover glass, j^-^ of an inch thick, perfectly 

 transparent to the ordinary rays of light, throws as strong a 

 shadow as a board one inch thick. The bones of the hand 

 throw a stronger shadow than the flesh surrounding them. 



