394. HAT B. Fineand W. F. Magie—Glow Discharge. 
has been found in the Tertiary aspect of the mollusks, most of 
which are fresh or brackish-water forms. Hitherto little has 
been known of the fresh-water fauna of the undoubted Creta- 
taceous, but if this should prove to have, as now appears proba- 
ble, a “ Tertiary” aspect throughout, it will tend to break 
down the molluscan eyidence of the Tertiary age of the Lara- 
mie, and unite this formation still more closely with the 
underlying beds. 
Montreal, March 1, 1881. 
Art. LIL—On the Shadows obtained during the Glow Dis- 
charge; by H. B. Fine and W. F. MaGre. 
It is well known that a body interposed between the poles 
of a Holtz machine causes a so-called electrical shadow to 
appear upon the positive glow. We believe, however, that 
the fact that a similar shadow can be obtained upon the 
negative glow has not yet been published. These appearances 
seemed of some importance as offering a further proof of the 
essential similarity of the positive and negative discharges. 
The following points with reference to them may be of some 
interest. 
e glow was best obtained on either electrode when the 
simultaneously. The observations of Professor Wright* on 
the positive a were verified and found to hold for the 
negative also; and, in fact, all the phenomena obtainable with 
the one were likewise characteristic of the other. ; 
ese shadows, in general, whether positive or negative, 
represent closely the outline of the interposed object. If, 
however, the lines of electrical action be deflected by the 
presence of a conductor, the form of the shadow is altered. 
e could not effect any such alteration by merely blowing 
across the field. 
The size of the shadow varies with the tension on the 
electrode, becoming smaller as this is heightened. This fact 1s 
* This Journal, II, xlix, 381. 
