Up to quite recently, Luke Howard’s division of clouds, formulated in 1802, held first place; even now it is in constant use, for though attempts have been made at a more scientific classification, all of them, with the single exception of that proposed by the late Rev. Clement Ley, can only be termed make-shifts. Mr. Ley’s classification, unfortunately, is long, and not well adapted to the use of any but professional investigators, or enthusiasts with ample time on their hands. There exists a so-called “international” system of cloud nomenclature, but, for all that, each country has its own especial system, with the result that vast collections of cloud statistics are of little value as helps to a classification, and are useful only as records of clouds present at certain times. Clouds owe their existence to two causes: 1. Through the passing of warm, moist air into colder, when, owing to condensation, a certain proportion of the moisture becomes visible in the form of a cloud. 2. Through changes occurring in the atmosphere as it rises into higher regions of atmosphere, where decrease in pressure and expansion and consequent loss of heat take place and cause condensation of moisture. The first process may be described as the condensation formation of clouds, and the second as the adiabatic formation of clouds. As a matter of fact, no hard and fast line separates these two operations; they act in unison, and the combination of vertical and horizontal currents goes to make up the diversity of forms which clouds assume. In settled states of the atmosphere, Stratus clouds are common, or the sky may be clear. In unsettled conditions, Cumulus or Heap clouds are formed. We shall now describe a few familiar forms of cloud, giving them simple names and endeavoring to compare them with other nomenclatures. Of Cumulus clouds there are five well-defined varieties. _Rain Cumulus_, of which there are two sub-varieties: (_a_) Shower-cumulus, when rain falls from the cloud without increment of wind. The edges of this cloud are not cirrus-topped. (_b_) Squall-cumulus, when the rain is accompanied by wind, or by wind with hail and snow falling from this cloud. In these cases the Cumulus cloud is generally much serrated, having a cirriform edging. In some cases this cirriform edging extends far over the sky and forms halos, particularly at the rear. Two rarer varieties of Cumulus are: _Pillar-cumulus_, generally noticed over the calm belts of the ocean, and distinguishable by its slender forms, which rise to great altitudes. _Roll-cumulus_ generally accompanies strong winds, particularly polar west winds, which succeed cyclonic disturbances. Here we have the ordinary Cumulus cloud so blown along by the wind as to assume the roll formation from which it is named. A still rarer form of Cumulus appears in scattered patches over the sky, and is indicative of an electrical state of the atmosphere.