Intelligence and Miscellaneous Articles. 229 



This enfeeblement increases up to a certain limit as the resistance is 

 increased, from which forwards it diminishes until it becomes insen- 

 sible. This would appear to prove, that to react upon the primary 

 the secondary requires to be retarded ; and that the greater the 

 amount of the retardation, up to a certain limit, the greater is the 

 enfeeblement. But by increasing the resistance we diminish the 

 strength of the secondary, and when a certain limit is attained, this 

 diminution is first compensated for by the influence of retardation, 

 from which point forwards with every increase of the resistance, the 

 enfeeblement of the primary is diminished. A primary current 

 which fuses a certain length of platinum wire where the ends of the 

 secondary are disunited, or where they are united by a thick wire, 

 fails to do so when they are united with a thin wire. But if, instead 

 of a thin wire, a body of much greater resistance, a column of water 

 for example, be introduced, the platinum wire is fused as before. 



XXVIII. Intelligence and Miscellaneous Articles. 



ON TABASHEER. BY M. GUIBOURT. 



'T^ABASHEER is a siliceous concretioii found in the interior of the 

 -•- stem of the large Indian Bamboo (Bambusa arundinncea, Schreb.). 

 The attention of the orientals was first directed to this substance by the 

 writings of the Arabian physicians. The Turks and Arabs only know 

 it under the name of Tabasheer, which is of Persian origin. In India 

 it has other names, such as Vedroo-paloo (bamboo-milk), Vedroo-car- 

 pooram (bamboo-camphor), and Mangil-upoo (bamboo- salt). The 

 orientals regard it as one of the most valuable medicines, whilst it 

 is only interesting to us from its being a concretion of silica depo- 

 sited in a vegetable organism, which has some resemblance to the 

 hydrophane of Haiiy. 



Towards the end of the last century, Macie stated that tabasheer 

 was nothing but silica. As, however, Vauquelin found it to contain 

 30 per cent, of potash and lime, Macie's determination was regarded 

 with doubt. Brewster has examined its optical and physical jiroperties. 

 The author has received a quantity of this substance from Professor 

 Royle, and submitted it again to analysis. The analysis gave — 



Silica 96-94 



Water 2-93 



Potash and lime 0'13 



Organic matter traces 



Tabasheer is imperfectly transparent, and sometimes perfectly 

 opake. When immersed in water a quantity of air-bubbles escape 

 from it, and it becomes more transparent ; hydrophane behaves in 

 the same manner. When completely saturated with water its spec. 

 grav. is as follows : — 



2-158, Macie; 2' 1 09, Cavendish ; 2-059 to 2-412, Brewster ; 

 and 2-148, Guibourt. 

 When tabasheer is weighed after soaking in water, it is found to 

 have more than doubled its weight. The statements put forward 

 upon this point are as follows : — 



