Sxey.— Oil as a Nucleus in Super-saturated Saline Solutions. 409 
scientists, I will now affirm that such facts are irreconcilable with this 
theory of theirs. 
The question I have started as to whether or no surface tension has an 
effect, even of a mere subsidiary character, in producing these nuclear 
effects described, I leave for solution to those physicists who for so many 
years have been working at the mechanical properties of liquid surfaces. 
But I must remark, ere I leave this part of my subject, in relation to the 
effect or non-effect of any specific oil in producing crystallization, that in 
regard to this, not only does the more or less resinous condition of an oil 
affect it, but also the more or less proneness it has to become resinoid upon 
exposure to air and water; and this brings us face to face with another fact 
elicited by these investigators. It is, that in dull, damp, and cloudy 
weather an oil may not produce nuclear effect ; whereas on a fine bright 
day it may be “ particularly active.” This they explain by supposing the 
surface tension of the solution to be lower upon cloudy than upon bright 
days. But in connection with my theory (the chemical one) I would point 
to the well-known fact, that light in conjunction with air favours the change 
of oil generally to resinous matter, and hence an acquirement of nuclear 
effect on bright days. 
Another and the last remark I have to make here is, that in all those 
experiments with oil where a nuclear effect is produced by these scientists, 
a flashing or spreading out of such oil from the lens-shape it may first 
assume, is the constant concomitant or antecedent. Now, this uniformity 
of action is misleading, for it impresses one with the idea that any oil which - 
spreads over the surface is one which will have, when fairly tried, a nuclear 
action ; and so it has the effect of prepossessing one unduly in favour of the 
tension theory. As a matter of fact, however, I find that gasoline, an oil of 
very feeble tension, too, spreads rapidly over such solution without pro- 
ducing any solidifying action, so it is not nuclear, thus breaking the 
uniformity hitherto observed. 
On the other hand, however, we may take it for granted that in every 
case where a nuclear action is exercised by an oil, there is more or less of a 
surface spread of the oil accompanying such action. 
And now in pursuance of the next part of my paper: it is relative to 
the mode of action of solid nuclei in super-saturated solutions, and is merely 
a description of certain results I have obtained thereon, while the subject of 
liquid nuclei was under consideration. Two of these results are, I believe, 
novel to scientists (Nos. 4 and 5). The others are got by repetitions of expe- 
riments by investigations which have often led to results diverging more or 
less from one another. They are recorded, not under the idea of settling a 
question about which there is great debate, but only as a small and possibly 
47 
