Ske:y, — On ToniUnson's Cohesion Figures. ' 491 



Secondly, as to the ground of tliese figures, i.e., the part in which these 

 annular spaces or markings are set. I found that when a small quantity of 

 any oil is gently placed thereon it does not spread to any notable extent, 

 but keeps nearly to the drop form ; and it was further manifested to me 

 that this part breaks into angular fragments, which are possessed of such 

 rigiditj^ that they kee^D to a tabular form no matter how they are dashed 

 about. Now, as oils indiscriminately flow over oils, and as none of them 

 can indurate to such an extent as would determine angular shapes to their 

 fragments, it is clearly demonstrated that this part, i.e., the ground of the 

 pattern, is not an oil. 



The current idea, then, as to the nature of this part of the figure, being 

 fallacious, it is necessary that we should adopt another. 



What this ought to be, a full consideration of the case will, I think, 

 clearly show. Thus, owing to the great proneness of oils generally to oxidize 

 to substances of a resinous nature when exposed to air, it is certain that in 

 no instance do we, for the production of these figures, operate with an oil 

 that is not, to a small extent, charged with such matters ; and further, it is 

 also as certain that the quantity of resinous matter therein must be very 

 largely increased by the time that any cohesion figure made with it has 

 passed to its final form. It being, therefore, undeniable that resinous 

 matter forms one of the principal constituents of the cohesion figure in its 

 ultimate condition, the conclusion forces itself upon us that of such matters 

 is the material of their ground alone composed. This is really the only 

 alternative, as it is one which meets all the requirements of the case. So 

 attenuated, indeed, and so exposed are the thinner portions of these figm'es, 

 and so rapidly is the kind of change indicated wrought upon oil under these 

 conditions, that it is only reasonable to conclude that these portions are 

 wholly composed of resin, to the exclusion consequently of any trace of oil. 



As being corroborative of the truth of the supposition that the presence 

 of resin in the cohesion figures plays an important part in their production, 

 I would inform you that the addition of about ten per cent, of resin to a 

 good oil very much quickens the production of cohesion figures, and also 

 passes them through their various phases to the ultimate figure with a 

 speed which is far gi-eater than is to be observed in the case of the oil. 



And now I think the foregoing statements of facts and observations may 

 be fahiy held to demonstrate — 



1st. That the annular spaces or markings of Tomlinson's cohesion 



figures are not depressions but protuberances, not holes but hillocks, 



and are not composed of water, but of oil. 



2nd. That the plane part of these figures the ground as it were of the 



pattern, is not oil (as heretofore quiescently allowed), but either a 



