n6 THE POPULAR SCIENCE MONTHLY. 



is upward, downward, or horizontal, according to the position of the 

 center of gravity at the moment of the experiment. M. Plateau has 

 clearly demonstrated that the normal position of this point varies with 

 each species. 



One very small group, the Cetoniaclce, fly with the wing-cases 

 down an interesting fact, for in this instance they act upon the axis 

 of suspension, and effect a step toward the state of complete differen- 

 tiation which we find in the following group. 



In the Diptera (mosquitoes, flies, etc.) the steering faculty reaches 

 its highest development. The second pair of wings is transformed 

 into organs having the special function of steering, the balancers or 

 poisers ; and these insects have accordingly a remarkable perfection 

 of movement. A single pair of wings does all the flying, and, as 

 they are not large, the diminution of the supporting surface is com- 

 pensated by greater rapidity of vibration. I have proved by experi- 

 ment that the balancers act by displacing the axis of suspension. 

 Suppress the balancers, and the flight becomes fatally downward, 

 because the normal and invariable position of the center of gravity 

 is in front of the axis of suspension ; the animal, therefore, can not 

 modify his movement in any way, the abdomen being but slightly 

 movable, and the balancers cut off. If, now, we come to his relief 

 and attach a tiny weight to his abdomen, just sufficient to carry the 

 center of gravity back to its normal place, we restore to the insect 

 the power to perform all his aerial evolutions. 



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SKETCH OF JAMES CLEEK MAXWELL. 



AMONG the present generation of English physicists none have 

 attained to greater eminence, or have made more valuable addi- 

 tions to this department of science, than the late Professor Maxwell. 

 The splendid promise that his accomplished work gave of future work 

 makes his death, at the early age of forty-nine, at the height of his 

 powers, an irreparable loss to science. An accomplished mathemati- 

 cian, an unexcelled experimenter, he was peculiarly fitted to carry on 

 those delicate researches in the domain of molecular physics by which 

 he made it his own, and in which he was without a. rival. Possessed 

 of a vivid imagination, he had that power of holding it well under con- 

 trol, and making it subservient to the conditions of scientific investiga- 

 tion, that belongs only to the highest types of mind, and which is essen- 

 tial to the best and most valuable work in science. Though possessed 

 of the power of direct and lucid exposition, he was never what is 

 termed a popular lecturer. The subjects he considered, and his con- 



