50 Aids to Microscopic Inquiry, 



hand moved through a small space, and the long end of the 

 lever through a larger one. Gain of power took place in the one, 

 and loss of it in the other, if such phraseology can be allowed. 



It is customary to speak of gaining or losing power by em- 

 ploying levers ; but our readers will understand that there is 

 not, strictly speaking, any loss or any gain, but simply a differ 

 rent mode of distributing power. Lever action is best illus- 

 trated by a steel-yard, in which one pound, four inches from 

 the point of support, will balance four pounds one inch from it 

 on the other side of the support. As much work is done when 

 four pounds are moved one inch, as when one pound is moved 

 four inches. All that the lever accomplishes is to enable us to 

 make practical equations of this sort. 



Suppose the steel-yard, balanced by the two weights, one 

 pound and four pounds, arranged as above stated. It will be 

 plain that if a slight addition is made to either weight the 

 balance will be disturbed. If added to the pound weight, it 

 will cause it to descend through a large space to make the 

 heavier weight rise through a little one. If added to the four- 

 pound weight, it will enable it, by traversing a small space, to 

 make the lighter weight move through a larger one in the same 

 time. Now, in Animal Mechanics, it constantly happens that 

 a small muscular contraction moves a long limb or a long jaw ; 

 and if the extremity of the limb or jaw is moved with much 

 power, it is evident that the muscular force exercised at such a 

 disadvantage must have been intense. Many microscopic 

 creatures are sufficiently transparent to enable the contraction of 

 their muscles to be distinctly seen, and the effect thereof noticed. 



In all cases of lever motion of limbs or jaws of microscopic 

 creatures, the position of the fulcrum and of the force should be 

 noted ; and if, as is often the case, the lever is a long one, and 

 overcomes considerable resistance, we gain an insight into the 

 strength of its material, as well as into the amount of muscular 

 force employed. The principle of the lever will explain why it 

 is easier to carry a long pole by the middle than by either end; 

 and it is curious to watch how insects, and other creatures who 

 have burdens to carry, find out by instinct or experiment how 

 to hold them, so as not to suffer from an erroneous disposition of 

 the weight. 



Wedges of various shapes occur in the mandibles and stings 

 of insects; and as saws and rasps are only modifications of the 

 wedge, the palates of mollusca afford another interesting set of 

 illustrations ; and there is likewise a very conspicuous one in 

 the elaborate saw of the saw-fly. Even the screw may be 

 traced in its use as a holdfast ; as a snail may bo said to 

 screw himself into the whorls of his shell, and thus obtain a hold 

 which enables him to drag it about. 



