THE CAPPED CUMULUS, OR ARCHED CROWN. 



Bv the Rev. S. BARBER, F.M.S. 



Rx.0} TlfcfcwT^^P" ^ I S phenomenon, 

 which is not very 

 unusual in thundery 

 weather, when the 

 storm is gathering 

 or passing away, is 

 interesting as being 

 indicative of the 

 extent to which the 

 electrical masses af- 

 fect the contiguous 

 atmosphere. When 

 highly charged piles 

 of cumulus are seen 

 drifting in the breeze, 

 at no great distance, 

 and exhibiting rifts 

 and chasms and 

 mountain crags 



about their precipi- 

 tous sides and sunny peaks, — wreaths of mist and 

 vapoury bands may be seen floating athwart the dark 

 sides and rolling upwards toward their summits. This 

 foggy vapour holds off from the rock-like sides of the 

 towering cumulus (with which it refuses to coalesce), 

 and gives to the latter an appearance of great solidity. 

 Often maintaining its isolation, it spreads over the 

 topmost crests in a thin, loose strip of vapour, and, 

 bending down the opposite side of the cloud, forms a 

 complete detached arch. At times this arch has the 

 appearance of being highly condensed ; and, allowing 

 for the height of the species of cumulus to which 

 it attaches itself, the intervening space of clear sky 

 between the two clouds must often be of considerable 

 dimensions. 



There can be little doubt that the cap or arch 

 formed in this way has a form which corresponds to 

 that of the larger cloud. At times, however, the 

 appearance may be one of perspective only, as may 

 be seen when there are short strips or thin lines of 

 No. 169. 



condensed stratus lying among the cumulus. These, 

 particularly in unsettled weather, have their ends 

 sometimes bent downwards, as if attracted by the 

 earth.* In passing, we may say that this latter form 

 of cloud (which is closely allied to the cumulus- 

 " cap ") is seen generally before rain storms, and 

 often precedes violent squalls. It is seen occasionally 

 in parallel bands. 



Whether the form of the vapour which crowns the 

 summit of a cloud-pile results from the radiation of 

 electrical force acting at a certain distance, or is 

 merely the effect of condensation caused by the chill- 

 ing effect of the cloud mass on the surrounding air, 

 is an interesting though a difficult matter to determine ; 

 the relations existing between different masses of 

 cloud not having yet much engaged the attention of 

 meteorologists. Even when these masses are similar 

 in species there is much difficulty ; but the difficulty 

 is greater when those species are different, e.g., those 

 of stratus and cumulus, as in our present subject. 



It has been remarked by Maury and other writers, 

 that the sudden formation of hail or snow must often 

 be attended by a noticeable increase in the temperature 

 of the surrounding atmosphere, and the fact has been 

 so recorded. This increase of temperature is in agree- 

 ment with, and indeed corroborates, the mechanical 

 theory of heat so fully enunciated by Tyndall in his 

 interesting work on "Heat as a Mode of Motion." 

 The part which electricity plays in regard to the 

 origin of the stifling and oppressivef atmosphere that 

 precedes thunderstorms must be very powerful, 

 whether acting directly or indirectly. 



It has been noticed that the passage of a large 

 bank of cirro-cumulus will often cause a remarkable 

 dropping of the temperature of the air beneath ; and 

 (allowing this to be true) we can only account for the 



* Probably it is merely a more condensed variety of that 

 which forms our present subject. 



T There can be little doubt, however, that the sensations 

 many persons experience before a storm result from the direct 

 action of the electricity in the body. 



