378 



Improved modification of Dr. Locke's Galvanometer. 



m 



Culm 6 — 10 inches high, triquetrous, smooth, leafy towards the 

 base ; leaves flat, soft, sheathing, upper ones long as the culm ; stig- 

 mas three ; spikes three or four, sub-umbelform, upper one oblong, 

 staminate below ; the others pistillate, ovate or oblong, subsessile, 

 bracts longer than the culm ; fruit oval, roundish, triquetrous, orifice 

 entire, light green ; scale ovate or oblong, acute or somewhat obtuse 

 on the same spike, shorter than the fruit, and black. 



Found in Alpine meadows of Lapland ; and by Dr. Richardson, 

 on the Rocky mountains, and also at the sea-coast of the Arctic re- 

 gions of America, full in fruit June, 1826. 



Figures of two Carices are in this volume ; 



C. Baldwinia, D. Tab. T. fig. 61. 



C. venusta. do. 



62. 



Art. XV. — Communications by Dr. John Locke, of Cincinnati 



I. Improved modification of Dr. Locke's Galvanometer. 



Cincinnati Female Academy, Feb. 14, 1834. 



TO PROFESSOR SILLIMAJST. 



V 



•In my last, I sent you some account of my galvano- 

 meter as finally made in the discoid form on a wooden ring. My 

 communication was accompanied by a drawing of the instrument 

 as enclosed in a cylindrical box. I now communicate to you an im- 

 provement which I have since made by adding a stationary magnet 

 to neutralize the effect of the earth's magnetism on the needle. 

 This magnet I have adapted to the brass tube which rises from the 

 center of the glass cover, and encloses the filament suspending the 

 needle. It is two and a half inches long, 

 and one eighth of an inch in diameter, 

 having a large perforation in the middle, 

 in which is inserted a short piece of 

 brass tube having an inside diameter 

 adapted to the suspension tube of the in- 

 strument. The tube and the magnet thus 

 connected surmount the instrument with 

 an ornamental cross. T The suspension 

 tube. P the ivory pin for winding the ' For <he drawing of the rest of 



.. ._V ii • j this instrument, see p. 105 of thi» 



filament by which the needle is suspend- volume. 



