j270 PORTABLE ELECTROMEfER. 



quently examined the roots with attention, both in an entire 

 state and when dissected, but could never perceive the 

 smallest difference between them, and those of healthy 

 plants. 



With the hope that the subject will be further investis^ated 

 by those whose leisure affords them opportunity, and whose 

 abilities are adequate to the inquiry, 

 I remain, SIR, 



Your obedient humble servant, 

 Chohham, Oct. 1, 1807. ROBERT HARRUP. 



vr. 



Description of a simple and convenient portable Electrometer 

 for Mineralogists. In a Letter from a Correspondents 



To Mr. NICHOLSON. 

 SIR, 



trometer. 



Portable elec- JLjOOKING over Brongniart's Treatise on Mineralogy, 

 lately published at Paris, ft appeared to me, that the elec- 

 trometer he has figured and described for the purpose of de- 

 tecting electricity in minerals deserves to be better known 

 than I imagine it is ; its simplicity rendering it very porta- 

 ble, and always ready to use, without being liable to be out 

 of order. If you entertain the same opinion of its conve- 

 nience to the mineralogical traveller, perhaps you may find 

 a corner for it in some plate or other of your valuable and 

 useful publication. 



I am, SIR, 



Your obliged reader, 



O. N. 



Method of de- To discover the production of electricity in a stone by 

 ^^TV'' ft^^^^"' heat or friction, it is brought near to either end of the slen- 

 der brass needle, a h, PI, VIII, fig. 2, and whatever kind 

 of electricity the stone has acquired, it will make the needle 

 ttiove, if this be done with proper precaution. 



. But 



