o sets of
observations, with three or four minutes' interval between them; and, if
the distance from the point of suspension to the centre of the stone be
thirty-nine inches, and if the string be thin and the stone very heavy,
it will beat seconds very nearly indeed. The observations upon which the
longitude of the East African lakes depended, after Captain Speke's first
journey to them, were lunars, timed with a string and a stone, in default
of a watch.

Hour-glass.--Either dry sand or water may be used in an hour-glass; if
water be used, the aperture through which it runs must, of course, be
smaller.

CLIMBING AND MOUNTAINEERING.

Climbing.--Climbing trees.--Colonel Jackson, in his book, 'How to
Observe,' gives the following directions for climbing palms and other
trees that have very rough barks:--"Take a strip of linen, or two towels
or strong handkerchiefs tied together, and form a loop at each end, for
the feet to pass tightly into without going through; or, for want of such
material, make a rope of grass or straw in the same way. The length
should embrace a little more than half of the diameter of the trunk to be
climbed. Now, being at the foot of the tree, fix the feet well into the
loops, and opening the legs a little, embrace the tree as high up as you
can. Raise your legs, and pressing the cord against the tree with your
feet, stand, as it were, in your stirrups, and raise your body and arms
higher; hold fast again by the arms, open the legs, and raise them a
stage higher, and so on to the top. The descent is effected in the same
way, reversing, of course, the order of the movements. The ruggedness of
the bark, and the weight of the body pressing diagonally across the trunk
of the tree, prevent the rope from slipping. Anything, provided it be
strong enough, is better than a round rope, which does not hold so fast."
A loop or hoop embracing the body of the climber and the tree, is a
helpful addition. Large nails carried in a bag slung round the waist, to
be driven into the bare trunk of the tree, will facilitate its ascent.
Gimlets may be used for the same purpose. High walls can be climbed by
help of this description; a weight attached to one end of a rope, being
first thrown over the wall, and the climber assisting himself by holding
on to the other end. Trees of soft wood are climbed by cutting notches
two feet apart on alternate sides. Also by driving in bamboo pegs,
sloping alternately to left o