‘288 Prof. Challis on the Phenomena of 
that a particular specified value (2;*) of #* may be equal toc, a 
and c being given. My results are shortly stated in the Fourth 
Report of the British Association, p. 528. The question 
bears closely on the subject of the solution of equations in- 
volving surds and their “ chance” of representable roots, a 
subject which was treated in an interesting and logical man- 
ner by Mr. W.G. Horner in a letter to be found, p. 43, of 
the January Number of your Magazine for this year. I hope 
also that you will be able to find room for a statement of the 
restrictions which various ordinary exponential theorems re- 
quire, and for a few useful equations and developments. 
With sentiments of sincere respect, I have the honour to be, 
Gentlemen, yours, &c., 
Inner Temple, Feb. 12, 1836. Joun T. GRAvEs. 
LVIII. On the Phenomena of Drops of Oil floating on Water. 
By the Rev. Professor Cua.uis.* 
AM not aware that the following facts, connected with the 
subject of capillary attraction, have been before observed. 
A single drop of salad oil was let fall on the surface of water 
contained in a glass tumbler, and was seen to spread imme- 
diately on the water surface. Another drop let fall shortly 
after on a part of the surface not reached by the spreading of 
the first, was not observed to spread in the least degree like 
the other, but instantly assumed a well-defined circular shape. 
The first drop also collapsed by degrees into a circular form ; 
and this, it was found by repeating the experiment, was most 
likely to happen when the drop was not of very small size. 
When two drops fell in very quick succession, both of them 
were observed to spread, but that which reached the surface 
last, spread in less degree than the other, and sooner assumed 
a circular shape. The smaller the size of the spreading drops, 
the greater appeared to be their tendency to spread. In one 
instance a very small drop was seen to be succeeded by an- 
other ata considerable interval, which also spread, but in 
much less degree. These phenomena were uniformly pre- 
sented in a great number of trials, fresh water being put into 
the glass after each. The chief thing to remark is, that without 
any visible connexion between the first drop and the succeed- 
ing ones, the manner in which the latter are affected on coming 
into contact with the water is influenced by the previous con- 
tact of the first. 
The explanation I propose to give of this fact will be drawn 
* Communicated by the Author. 
