150 
POPULAK SCIENCE KEVIEW. 
and if it be one of those branded K. 0., that is to say, one that 
has been tested at the Kew Observatory, so much the better. 
In reading thermometers, care must be taken to avoid the dis- 
turbing influence of the heat radiated from the observer’s body ; 
that is to say, the observer must approach his instruments, read 
them as quickly as possible, and retire again, especially taking 
care to hold his breath. 
Clouds. — The indications of clouds are, when rightly under- 
stood, more important than might be supposed. 
Howard first reduced them to an orderly classification, and his 
nomenclature is now generally accepted. The following is an 
epitome of it : — 
There are three primary forms of cloud and four secondary 
ones. 
Primary Forms . — 1 . Cirrus . — Fibres extensible in various 
directions : these fibres often resemble feathers, wisps or locks 
of hair. Generally seen in groups after severe weather, and 
when the air is in gentle motion. The highest of all clouds. 
2. Cumulus . — A cloud formed of dense aggregations of con- 
vex masses, rising from a horizontal base into irregular moun- 
tainous rocky heaps, often with white snowy woolly tops. It 
characterises dry, fine summer weather. Before rain, it ap- 
proaches the earth and becomes more dispersed, and the woolly 
features more prominent. 
3. Stratus . — An extended continuous stratified aggregation. 
It forms at sunset, and disappears at sunrise. The lowest of 
all clouds. 
Secondary Forms. — 4. Cirro-Cumulus. — Cirrus fibres com- 
pressed in rounded masses or woolly tufts, disposed, in a measure, 
horizontally. In warm and dry weather, and especially in sum- 
mer, it floats at different heights in detached rounded groups. 
5. Cirro-Stratus. — Cirrus fibres, as if squeezed together by 
forces operating above and below, which results in a stratifi- 
cation. Solar and lunar halos, mock suns, and mock moons 
display themselves in clouds of this class. 
6. Cumulo- Stratus. — Cumulus and stratus clouds inter- 
mingled. Large fleecy cumuli rising from or seemingly pierced 
by stratus clouds. When black or bluish near the horizon, it is 
passing into — 
7. - Nimbus. — A dense continuous sheet of almost uniform 
black or grey tint with fringed edges. This is the rain-cloud. 
The rainbow belongs to it. 
Small stray fragments of cloud floating about in the air are 
termed scud. In noting clouds, it is sufficient to designate them 
by the numbers above, to save space and trouble. Daily records 
should be taken, if possible about 9 a.m. and 3 p.m., of the 
