Formed by the collapse of cumulus or strato-cumulus. A cloud of evening, easily recognized as lenticular patches. S. L. 5. _Strato-cumulus_ (Plates 38 and 39). A term applied to either a stratus which has thickened every here and there into cumulus, or a number of cumulus which have joined together so as to show a nearly continuous common base. S. Cu. GROUP CUMULUS. 1. _Cumulus minor_ (Plate 43). Small cumulus. Cumulus clouds so small as to present the appearance of rounded lumps, no definite pyramidal form or flattened base. Cu. Mi. 2. _Cumulus major_ (Plates 44 and 45). Large cumulus. Characterized by a flattened base and rounded clear-cut upper surfaces. Cu. Ma. 3. _Cumulo-nimbus_ (Plates 49 to 52). Storm cloud. Characterized by the expanded, anvil-shaped, or disc-shaped top, cirrifying at its edges. GENERAL TERMS _Nimbus_, a term applied to a cloud from which rain is falling. When the form of the cloud is visible, the term should be attached to that belonging to the cloud. It may, however, be used as a substantive alone when there is nothing to show from what sort of cloud, or combination of clouds, the rain is falling (Plates 35 and 36). Nimbus is either heavy stratus, massive strato-cumulus, or a combination of these with stratiform clouds above, and possibly ragged masses of fracto-cumulus below. N. either alone or after the sign of the cloud. _Fracto-_ is a term placed as a prefix before the name of a cloud to indicate that the cloud has ragged irregular margins, as if it had been more or less torn to pieces. It is sometimes less awkward to append the word fractus after the name of the cloud. A convenient abbreviation would be to write F. after the name of the cloud. _Undatus_, or waved, should always be added to the name of any cloud which shows the arrangement so described. CHAPTER XI CLOUD PHOTOGRAPHY REFERENCE has been made in the first chapter to the fact that those who wish to make a photographic study of clouds must follow a special course of procedure. For every photographic purpose there is some particular process or some special kind of apparatus which is better fitted for the end in view than any other, and half the difficulty in attaining success is to find out the best tools and the best methods.