556 FORMATION OF A MACKEREL SKY. 



In conclusion, I have to express my indebtedness and thanks to 

 Mr. Ellery and to Mr. Russell for advice and assistance in pre- 

 paring this statement of the theory. Mr. Russell has most 

 generously allowed me to make use of his photographs and of the 

 notes which he made at the time of the phenomenon. 



The ripple-cloud, or wave-cloud, or, to coin a corresponding 

 term, Undulus, should take its place in the classification of clouds 

 by the side of the Stratus, Cumulus and Cirrus, for out of 

 combinations of these elemental forms can be derived most of the 

 diversified and ever-changing cloud-groups which never cease to 

 delight and astonish the eye and mind of man. 



