THE YOUNG SCIENTIST. 
89 
flows through the bindmg-screw d, then Marvels of Pond Life —XL 
througii the coils on the arms of the U, L^^,™™,.^ , ^ rr . i tt 
4- ^-Kv,^,,^!. «r.rv.of,n,^o f ' C C ATTEKED about Hampstead Heath 
thence to a, and through the armatuie to ^ number of little pools, not big 
circuit breaker b, and back to battery j enough to be dignified by the name of 
through the binding screw e. The com- j ponds. They are generally surrounded 
pletion of the circuit makes a magnet of i J>.y f^^ze bushes and would escape atten- 
.. , , ^, ^ ^ ,n tion if not actually looked for. Those 
the U and draws the armature to itself, | which are mere puddles, and have only a 
and by doing so, breaks the circuit be- ' brief existence in rainy weather, seldom 
ELECTKIC BELL. 
tween the armature and spring b, which 
causes the magnet to lose its power, thus 
enabling the spring on the armature to 
return it to its normal position, which 
completes the circuit, and the operation 
is again repeated and so on, while the 
battery is connected. Your electric bell 
is now complete, and at some future time 
I hope to tell you of its practical uses. 
Geo. Thompson. 
Maiden, Mass. 
reward the labor of investigation; but 
others are permanent, except after pro- 
longed drought, and afford convenient 
situations for the growth of conferva?, 
star-weed, and other plants. These will 
nearly always repay the microscopic col- 
lector during the winter, when he must 
break the ice to get at their contents ; in 
spring, when loug chains of frog-spawn 
afford ocular evidence of the prolific pro- 
perties of the Batrachian reptiles ; and in 
summer, when they afford both shade and 
sunshine to their numerous inhabitants. 
Small beetles, water-spiders, larvae of 
