154 
be found a number which is the hypotenuse. Then, as this 
number is to 10, so is the number obtained by the first 
method to the true number. 
Thus, to take the first illustration, of 0'5 in 5 inches : this 
is equal to 1 in 10. The hypotenuse of 1 in 10 (see table) 
= 10'04987. Now, 01 inch was the result obtained. Then, 
as 1004987 ; 10 : ; 01 ; 0 09955, which is the true vertical 
rise. 
I had no little difficulty in my first efforts to restrain the 
excessive oscillations of the ether column, owing to the 
almost constant fluctuations of draught in flues. To obviate 
this the tube was choked to a narrower bore at the bend. 
This proving insufficient, I overcame the defect by the very 
simple means of inserting a piece of sponge at this part. 
It is perhaps needless to add that it is necessary to 
employ Mr. Fletcher’s tubes for insertion into the flue, and 
also his tables. 
Settle Cave Exploration. 
Mr. W. Boyd Dawkins, F.R.S., described the results of the 
preliminary investigation undertaken by the Settle Cave 
Exploration Committee. The cliffs of mountain limestone 
in the neighbourhood of Settle are penetrated by numerous 
caves, some of which are empty, some traversed by water 
which is silting up their lower chambers, while others have 
been filled in some places up to the very roof with debris of 
various kinds. All these caves have been at some time or 
other subterranean watercourses, and have been formed 
partly by the friction of the substances brought down by 
the stream, but principally by the chemical action of the 
carbonic acid in the rain water by which the insoluble 
carbonate of lime of the rock is converted into the soluble 
bicarbonate. Some have been inhabited at various time®, 
by man and wild beasts, and therefore may be expected 
to furnish valuable evidence of a condition of things 
