the summits of
mountains, it may be distinguished by the name of Fracto-stratus. See
fig. 8.

The scheme also provides that where a stratus or nimbus takes a lumpy
form, this fact shall be described by the adjective _cumuliformis_,
and if its base shows downward projecting bosses the word _mammato_ is
prefixed.

Issued as it has been with the authority of an international congress of
specialists, this scheme has been generally accepted, and must be
regarded as the orthodox system, and for the great majority of
observations it is quite detailed enough. But it does not give universal
satisfaction. Cirrus clouds, for instance, exhibit many forms, and these
so diverse that they must be due to very different causes. Hence for the
minuter study of cloud forms a more elaborate scheme is still needed.

Hence in 1896 H. H. Clayton of the Blue Hill observatory, Massachusetts,
published in the _Annals_ of the astronomical observatory of Harvard
College a highly detailed scheme in which the International types and a
number of subdivisions were grouped under four classes--_stratiforms_ or
sheet clouds; _cumuliforms_ or woolpack clouds; _flocciforms_, including
strato-cumulus, alto-cumulus and cirro-cumulus; and _cirriforms_ or
hairy clouds. The International terms are embodied and the special
varieties are distinguished by the use of prefixes such as tracto-cirrus
or cirrus bands, grano-cirro-cumulus or granular cirrus, &c.

Again in 1904 F. L. Obenbach of the Cleveland observatory devised a
different system, published in the annual report, in which the
International types are preserved, but each is subdivided into a number
of species. In the absence of any atlas to define the precise meaning of
the descriptions given, neither of these American schemes has come into
general use.

Further proposals were put forward by A. W. Clayden in _Cloud Studies_
(1905). His scheme accepts the whole of the International names which he
regards as the cloud genera, and suggests specific Latin names for the
chief varieties, accompanying the descriptions by photographs. The
proposed scheme is as follows.

_Genus._ _Species._

Cirrus Cirro-nebula Cirrus haze.
Cirro-filum Thread cirrus.
Cirrus Excelsus High "
" Ventosus Windy "
" Nebulosus