162 PICTURING MIRACLES 



Fortunately, my native boys in the launch above 

 me were experts in noticing the approach of sharks 

 and all the other dangers of the sea. They had con- 

 tended with them all their lives, but none came near, 

 so I had no trouble. 



The things I saw were so unusual, so interesting, 

 so absorbing, that to wander around in perfect com- 

 fort and examine them was a most wonderful privi- 

 lege. Anyone could do as I did with just the helmet, 

 which although too heavy to stand under on land, 

 under sea did not bother any more than my hat. It 

 opens an entirely new and delightful field for re- 

 search work. 



The camera work itself I soon found had many 

 difficulties to overcome. The correct focus and ex- 

 posure, which seldom trouble for land work or un- 

 der the microscope, gave all sorts of trouble under 

 sea. The focusing scale set for the measured distance 

 would be off ten actual feet meant setting it for six 

 to get sharp results. The exposure made on land the 

 same day, would be far too much under sea. I had 

 troubles aplenty until I remembered that the speed 

 of a lens was the ratio of its aperture to its focal 

 length, so what really took ten feet focus by the 

 scale on land, only took six under sea. I had short- 

 ened its focal length, speeding it up in that ratio. 

 Then on land, the closer the subject is to the lens, 



