74 
HINTS TO TRAVELLERS, 
For all practical purposes these rules are "sufficiently exact, but, 
owing to the slight variation of the length of the degree latitude, 
it is not absolutely correct for all latitudes. Should it be required 
to get the scale in statute miles to the inch, it will only be neces¬ 
sary to substitute 63,360 for 72,996, and the same rules will then 
apply. 
