Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 363 



the form of a very perfect ring. The volutes are the effects of 

 an optical illusion arising from seeing through a number of the 

 segments which compose the ring on either side, while at the 

 front and back of the ring the edges only of the segments are 

 seen. Figures of this type, with variations in detail, which it 

 would take too long to describe, are produced in cold castor oil 

 by oil of cinnamon, creosote, carbolic acid, sulphuric acid, sul- 

 phate of indigo, and glycerine. 



In a column of olive oil a drop of creosote, of carbolic acid, 

 of oil of cinnamon, or of eugenic acid is similarly penetrated 

 from below. Other oils, however, in olive oil are penetrated 

 from above. For example, a drop of croton oil descends at first 

 as a bulb and stem, the stem, as before, being moored to the 

 surfaee*. The bulb flattens out into the form of an oblate sphe- 

 roid, and in attempting to flatten still more it gets turned over 

 at the upper part into the form of a ring, but presenting the 

 appearance shown in A ; the medium closes in upon the open- 

 ing, which becomes deeper, as in B and C, until at length it 

 penetrates to the bottom of the spheroid, forming a trumpet- 

 shaped mouth as in D. In doing so it unites with the stem, 

 which thus appears to. have penetrated to the very bottom of the 

 spheroid ; while, to supply its length, the medium licks over the 

 outer surface of the spheroid, as in the former case, and thus 

 allows the stem to accompany the altered spheroid to the bottom 

 of the vessel. This series of processes, which it takes so long to 

 describe, may be understood at a glance by a reference to the 

 figures A to D. 



In some cases, instead of the voluted figure, the opening from 

 below is pyriform, and as the spheroid descends the pear-shaped 

 figure describes a circle within the spheroid, which gives it the 

 appearance of rocking to and fro upon its stem (see figs, a 1 , a?, 

 a 3 ). Thus while in a column of olive oil a drop of cinnamon or 

 of eugenic acid opens from below and forms a figure with volutes, 

 a drop of oil of cloves, or of creosote, or of carbolic acid is pene- 

 trated from below and a pear-shaped opening is formed within 

 the spheroid. We use the, word opening as we do the word 

 volutes, to express the appearances presented. The opening, 

 however, is a penetration of the spheroid by the medium in 

 which it is subsiding. 



In a column of lard at about 170° and upwards, a drop of oil of 

 cloves (and of some other oils) forms festoons and rings; but at 

 lower temperatures, as from 140° down to 82° (at which point 

 the lard used by me solidified), figures of the bulb-and-stem 

 type are formed. But in the case of castor oil there is some varia- 



* In the figures a portion only of the stem is shown. 

 2B2 



