494 



Sir William Thomson 



[Jan. 29, 



would have a radius of about 8 centimetres. If it were sulphate of 

 zinc alone, and of this magnitude, its period of vibration would be 

 about 5J seconds. 



Fig. 6. 



Fig. 7. 



Fig. 8. 



Fig. 9 shows a drop of sulphate of zinc floating on a wine-glassful 

 of bisulphide of carbon. 



In observing the phenomena of two liquids in contact, I have found 

 it very convenient to use sulphate of zinc (which I find, by experi- 

 ment, has the same free-surface tension as water) and bisulphide of 

 carbon ; as these liquids do not mix when brought together, and, for 

 a short time at least, there is no chemical interaction between them. 

 Also, sulphate of zinc riiay be made to have a density less than, or 

 equal to, or greater than, that of the bisul2)hide, and the bisulphide 

 may be coloured to a more or less deep purple tint by iodine, and this 

 enables us easily to observe drops of any one of these liquids on the 



