78 DR. H. B. GUPPY, ON CORAL ISLANDS. 
with sand and coral, but it is almost impossible to state in precise 
terms the changes since the visit of the Beagle, as the survey then 
made was little more than a sketch. The present Admiralty chart 
is of but little service in inquiring into past changes, for in it the 
original survey of the Beagle in 1836 has received several later 
additions, and there is nothing to distinguish the one from the 
other. For the purpose of navigation, and for the advantage of 
science, a complete examination of these islands should be made. 
The best season for surveying is during the calm weather of the 
months of January and February, when boats can venture close to 
the edge of the reef, and a satisfactory examination of the outer 
shores, as well as the interior of the atoll, can then be made. In 
collecting information from the residents, it will be necessary to 
remember that no records are kept in the islands ; and in studying 
past changes the observer will have to receive what may at first 
sight appear to be very interesting facts with scientific caution. 
Some corroboration of such facts should always be looked for, 
