Intelligence and Miscellaneous Articles. 235 



vitse, kingwood, ebony, and beech : rods made from most of these 

 (if free from cracks) had a remarkably clear metallic ringing sound 

 when struck ; those made from lignum vitse were very hard and of 

 exceedingly close texture ; those from beechwood best retained their 

 form, but differed from all others in contracting unequally in the 

 two directions across the grain of the wood, and, in consequence of 

 this, round tubes and crucibles became oval during the burning-pro- 

 cess. Rods made from lignum vitse and the other denser kinds of 

 material conducted electricity most admirably, and would probably 

 serve well for carbon pencils for the electric arc ; but if they had 

 been burned too rapidly their electric conducting-power was much less. 

 Of the four materials above mentioned, lignum vita? was the best. 



The following were found to be the chief conditions of success in 

 the process : — (1) vegetable materials of the hardest kind and closest 

 texture ; (2) wood of the straightest grain, free from knots and splits ; 

 (3) very slowly dried and heated ; (4) the heat very uniformly dis- 

 tributed ; (5) prolonged high temperature at the last ; and (6) gra- 

 dual cooling. 



Lignum vitse evolved a very large amount of oily and tarry matter 

 during the burning-process. . The charcoal from it had a remarkably 

 hard and shining surface, and two pieces of it rubbed together seemed 

 like too smooth stones ; it was also very heavy, and its texture was 

 so extremely close as to make it apparently quite impervious to 

 liquids : even after immersion in the strongest hydrofluoric acid its 

 surface had no acid taste ; it was feebly electro -positive to platinum 

 in strong nitric acid, and therefore would not equal platinum, if 

 substituted for it in a Grove's battery. 



By the appearance of each kind of charcoal, the kind of wood 

 from which it was formed could be distinctly determined, each wood 

 retaining its usual superficial markings. Some kinds cracked trans- 

 versely (for instance, boxwood and maple), others longitudinally 

 (thus ironwood and partridge-wood) ; others twisted ; some kinds 

 of charcoal w r ere very hard (coquilla-nut, lignum vitee, kingwood, 

 and ebony) ; those of ebony and kingwood acquired a purple colour 

 in places ; charcoal of beech and lancewood assumed a gentle curva- 

 ture ; those of walnut and maple were easily broken across ; those 

 of mahogany, pinewood, and walnut were soft; those of English and 

 Memel oaks were porous, &c. 



ON MAGNETO-ELECTRICAL MACHINES. 

 BY MM. JAMIN AND ROGER. 



In this research we have investigated, and believe we have suc- 

 ceeded in establishing, the laws of the production of electricity in 

 magneto-electrical machines. These machines may be characterized 

 by saying that they borrow from a motor, in the form of force, a 

 given quantity of heat, and that they reproduce it, through the in- 

 tervention of an electric current, in internal and external resistances. 

 The question to be solved was to find the laws which regulate the 

 quantity of heat borrowed on the one hand, and reproduced on the 

 other. 



