Dif] AND SYMBOLS. 75 



position of the. ocean waters are so thoroughly incorporated that, 

 far from altering its limpidity, they seem on the contrary to 

 increase it. In certain parts of the Arctic Sea shells are dis- 

 tinctly visible at a depth of 450 feet ; and in the Antilles, at 

 the same depth, the sea-bed is as distinct as if it were nigh the 

 surface. The sea grows turbid and yellowish only in those 

 regions where its bed is shallow muddy only where its agitated 

 waves stir up the sand and hold it in suspension. MY. 



A Natural Defence for the Defenceless. 



There are many kinds of "leaf-rolling" caterpillars, each 

 employing a different mode of rolling the leaf, but in all cases 

 the leaf is held in position by the silken threads spun by the 

 caterpillar. There are plenty of birds about the trees, and they 

 know well enough that within the circled leaves little cater- 

 pillars reside. But they do not find that they can always make 

 a meal on the caterpillars, and for the following reason : The 

 curled leaf is like a tube open at both ends, the caterpillar 

 lying snugly in the interior. So when a bird puts his beak 

 into one end of the tube, the caterpillar tumbles out at the 

 other, and lets itself drop to the distance of some feet, support- 

 ing itself by a silken thread that it spins. The bird finds that 

 its prey has escaped, and not having sufficient inductive reason 

 to trace the silken thread and so find the caterpillar, goes off to 

 try its fortune elsewhere. The danger being over, the cater- 

 pillar ascends its silken ladder, and quietly regains possession 

 of its home. CO. 



Degree makes all the Difference. 



"When a substance combines with oxygen, heat is evolved, 

 and if the union is rapid and fussy, light may be emitted as 

 well. The burning of a candle seems to be a very different 

 thing from the rusting of a nail ; but in truth the latter pro- 

 cess is simply a mild and dilatory species of combustion. It is 

 really a little conflagration, though it does not afford sufficient 

 heat to singe the wings of a moth, or sufficient illumination to 

 enable us to read a line. PO. 



