On the Influence of Atomic Weight. 461 



best-conductivity acid in the 5-in. basin over a revolving 

 electro-magnet turning about 3000 times a minute, was about 

 15° an hour ; in other words, the magnet went about 4,320,000 

 times as fast as the liquid; and the total possible error on the 

 supposition that the liquid is still, would be ^3-20000 °f *he 

 whole amount ; therefore it may be safely neglected. 



It appears, therefore, that the point to be borne in mind is 

 that the torsion must not be measured till the liquid has attained 

 its constant velocity; i. e. sufficient time must be allowed. This 

 velocity and this time will be less the greater the friction or 

 viscosity. But the introduction of glass threads, screens, or 

 porous plates to increase the friction would do more harm by 

 introducing uncertain electrical resistances than they could 

 possibly do good : the only device which seems as if it might be 

 of any use would be to make a jelly of the conducting liquid; 

 but this is quite unnecessary. 



We are engaged in measuring the conductivity of liquids by 

 means similar to those above shown. 



Explanation of Fig. A (page 453). 



Curve 1. The abscissae are in proportion to the velocities of rotation of 

 a permanent steel magnet beneath a copper disk ; the ordinates are in 

 proportion to the angles at which the disk comes to rest. This curve 

 appears to be a straight line, showing that the torsional moment is pro- 

 portional to the velocity. 



Curve 2. The abscissae are in proportion to the distances between a thin 

 copper disk and the upper surface of a permanent steel magnet revolving 

 beneath ; corrected for rate according to curve 1, the ordinates are in pro- 

 portion to the angles at which the disk comes to rest. 



Curve 3. The abscissae are in proportion to the diameter of a thin 

 copper disk, varying from 1 in. to 3*5 in. in diameter, turned by a revolving 

 permanent magnet beneath, 2 in. long ; the ordinates are in proportion to 

 the angular deflexions. The double line shows the secondary observations 

 about the region (the " pole ") of the magnet where the effect of variation 

 of diameter should be most marked. About this place there is an altera- 

 tion in flexure. 



LV . Influence of Atomic Weight. By Thomas Carnelley, 

 D.Sc.y Assistant Lecturer on Chemistry in the Owens Col- 

 lege. 



[Concluded from p. 381.] 



T/ISCOSITY, or the Transpiration of Liquids. — This is the 

 term applied to the passage of liquids through a fine capil- 

 lary tube under pressure. Poiseuille, who first made experi- 

 ments on this subject, was unable to find any connexion between 

 the rate of flow and the chemical composition of the substance, 

 because he used percentage solutions instead of solutions pro- 



