[93] Rech. sur la Force Absolue des Muscles des Invertébrés. I^e Partie. Mollusques Lamellibranches. Bull. Acad. Roy. de Belgique, 3^e Sér., Tom. VI. (1883). Do., II^e Partie. Crustacés Décapodes. Ibid., Tom. VII. (1884). [94] _Statical muscular force_ and _Specific muscular force_ are synonymous terms in common use. _Contractile force per unit of sectional area_ gives perhaps the clearest idea of what is meant. The comparison between the muscular force of Insects and large animals is sometimes made in another way. For example, in Carpenter’s Zoology[95] the spring of the Cheese-hopper is described, and we are told that “the height of the leap is often from twenty to thirty times the length of the body; exhibiting an energy of motion which is particularly remarkable in the soft larva of an Insect. A Viper, if endowed with similar powers, would throw itself nearly a hundred feet from the ground.” It is here implied that the equation Height of Insect’s leap Supposed ht. of Viper’s leap (100 ft.) ----------------------- = -------------------------------------- Length of Insect Length of Viper should hold if the two animals were “endowed with similar powers.” [95] Vol. II., p. 203. The calculation here quoted is based upon an observation of Swammerdam, who relates that a Cheese-hopper, 1/4 in. long, leaped out of a box 6 in. deep. But it is known that the work done by contraction of muscles of the same kind is proportional to the volume of the muscles (“Borelli’s Law”),[96] and in similar animals the muscular volumes are as the weights. Therefore the equation Work of Insect Work of Viper ---------------- = --------------- Weight of Insect Weight of Viper will more truly represent the imaginary case of equal leaping power. But the work = weight raised × height, and the weight raised is in both cases the weight of the animal itself. Therefore Wt. × Ht. Wt. × Ht. --------- (Insect) = --------- (Viper), Wt. Wt. and Ht. (Insect) = Ht. (Viper). The Viper’s efficiency as a leaping animal would, therefore, equal that of a Cheese-hopper if it leaped the same vertical height. Therefore, if the two animals were “endowed with similar powers,” the heights to which they could leap would be equal, and not proportional to their lengths, as is assumed in the passage quoted. [96] Haughton’s Animal Mechanics, 2nd ed., p. 43. Straus-Dürckheim observes that a Flea can leap a foot high, which is 200 times its own length, and this has been considered a stupendous feat. It is really less remarkable than a schoolboy’s leap of two feet, for it indicates precisely as great efficiency of muscles and other leaping apparatus as would be implied in a man’s leap to the same height, viz., one foot.[97] [97] In any comparison it is necessary to cite not the height cleared by the man, but the displacement during the leap of his centre of gravity.