1895 - 96 .] 
Mr John Aitken on Clouds. 
95 
cirrus are frequently observed with ripple markings on one or more 
sides of them just where the cloud is thin enough to be broken 
through by the eddies. If we watch these lenticular-formed clouds 
under these conditions, we frequently see the ripple markings 
getting nearer and nearer the centre as the cloud decays; and at 
last, when nearly dissolved, the ripple markings will be seen extend- 
ing quite across the cloud. It seems probable that “ mackerel ” 
and other cloud forms may be produced in the same way. 
The shapes which these ripple cirrus assume are much more 
varied than is generally supposed. I lately observed a most interest- 
ing form in the south of France while the mistral was blowing 
strongly. There were a few cirrus in the sky at the time, 
and one of these was rapidly being broken up into irregular 
ripple forms, but at one point there was formed a most perfectly 
cylindrical-shaped piece, its length being about twenty times its 
diameter. The whirling effect of the eddy was very evident by 
the circular streaking of the clouding. Further, this cloud was 
evidently hollow, that is, the interior was filled with clear air as the 
cloud was thinnest along the axis, and it had all the appearance of 
a revolving tube of cloudy air. 
It is not contended here that ripple clouds are never produced in 
the manner which has generally been accepted, only that so far as 
the writer’s observations go they have never been observed forming 
in the manner supposed. It is hoped that others will put the 
explanation here offered to the test of observation, and it is princi- 
pally with a view of getting others to repeat the observations that 
this has been written. 
HyIdres, 28 th March 1896 . 
