Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2- Appendix): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

276 APPENDIX. resemblance cannot be traced upon paper, because the edges are so ill-defined. It may also be called the ' Flat Cloud.' Nimbus is the heavy-looking, soft, shapeless cloud, from which rain is falling. Whatever shape a cloud may have retained previous to rain falling from it — at the moment of its change from vapour to water, it softens in appearance, and becomes the ' Nimbus,' or ' Rain Cloud.' Cumulus is the hard-edged cloud, or cloud with well-defined edges ; whose resemblance can be accurately traced on paper. This cloud is not, generally speaking, so large as the Stratus or Nimbus, aud appears to be a compact mass of either the former or latter, or of both. It may also be called the ' Heap Cloud.' These four classifications of clouds will not, however, suffice to describe exactly the appearance of the sky at all times. More minute distinctions are required, for which the following may be used : Cirro-stratus — signifying a mixture of Cirrus and Stratus. Cirro-cumulus- — Cirrus and Cumulus. Cumulo-stratus — signifying a mixture of Cumulus and Stratus. Which terms may be rendered more explanatory of the precise kind of cloud, by using the augmentative termination onus, or the diminutive, itus. Thus: — Cirronus, Cirritus ; C irrono- stratus ; Cirrito-stratus ; Cirrono-cumulus, Cirrito- cumulus ; Stratonus, Stra- titus ; Cumulonus, Cumulitus ; Cumulono-stratus, Cumulito-stratus. Should these be found insufficient to convey distinct ideas of every variety of clouds, the second word may be augmented or diminished, thus : Cirrono-stratitus, &c. These terms may be abbreviated for common use by MTiting only the first letters of each word ; allowing one letter to represent the diminutive, two letters the ordinary, or middle degree, and three letters the augmentative. As Cirrus and Cumulus begin with the same letter, it will be necessary to make a distinction between them by taking two, three, and four letters, respectively, of Cumulus ; thus, C, Ci., Cir. ; S., St., Str. ; N., Ni, Nim. : Cu., Cum., Cumu. Suppose it were desired to express Cumulito-stratoni, C.-Str. would be sufficient, &c.