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absorbed by a liquid remains constant, the weight 

 (volume multiplied by the density) of the absorbed 

 gas rises and falls in projx>rtion to its pressure. L. 

 of Definite Proportions, when two or more chemic 

 substances unite to form a compound, they do so in a 

 fixed and constant proportion. L., Delbceuf's, a 

 congenital variation of a number of individuals in a 

 species, if not advantageous or injurious, and if not 

 balanced by reversion, will produce a variety, the 

 proportion of which to the whole species tends to reach 

 equality. L. of Diffusion of Gases through 

 Membranes. See L., Graham'' s. L. Donders'. 

 See L. , Listing's. L., Dulong and Petit's, the 

 products of the specific heat of elements in the solid 

 state multiplied by their atomic weights are (approxi- 

 mately) the same ; i. e. , the atomic heat of elements 

 is (nearly) a constant. L. of Electrotonus, in 

 anelectrotonus the excitability and rate of nervous 

 conduction are diminished, while the electromotive 

 power is increased ; whereas in kathelectrotonus, the 

 excitability and rate of nervous conduction are in- 

 creased, while the electromotive power is diminished. 

 (Rutherford.) L. of Eccentric Sensations, that 

 wherever excitation occurs, whether in the nerve-cells 

 themselves or anywhere in the course of the nerves 

 leading to the cells, consciousness always refers the 

 sensation to the presence of some external cause of 

 excitement, i. e. , the power of conception always pro- 

 jects every sensation that reaches the consciousness 

 outward, that is, to where the cause of the excitement is 

 normal. (Rosenthal.) L., Faraday's : I. The quan- 

 tity of an electrolyte decomposed in a given time is pro- 

 portional to the strength of the current acting upon it. 

 2. The quantities of the substances decomposed are pro- 

 portional to their chemic equivalents. 3. The electro- 

 lyte must be a conductor. 4. The strength of the 

 electrolytic force is the same in all parts of the elec- 

 trolyte. L., Fechner's, the more expanded and 

 accurate statement of Weber' s Law as to the relation 

 between the intensity of stimuli and the changes 

 in the resulting sensations, a constant ratio exist- 

 ing between the strength of the stimulus and the 

 intensity of the sensation. With increase of the 

 stimulus the sensation increases only as the logarithm 

 of the stimulus. As there is a lower limit {threshold} 

 or liminal intensity of excitation, so there is an upper 

 or maximal height of sensibility. Between the two 

 is the Range of Sensibility. L., Fleischl's, of Con- 

 traction, that the excitability of a nerve varies at 

 different points in its course. L. of Functional Sub- 

 stitution. SeeZ., Vulpiari s. L., Gay-Lussac's. See 

 L., Charles's. L., Goodell's, Rule of Ready Practice : 

 " when the cervix uteri is as hard as one's nose, preg- 

 nancy does not exist ; when it is as soft as one's lips, 

 pregnancy is probable." L., Graham's, the rate of 

 diffusion of gases through porous membranes is in in- 

 verse ratio to the square-root of their density. L., Gud- 

 den's, lesions of the cortex do not give rise to lesions 

 of the nerves of the periphery. L., Haeckel's Fun- 

 damental Biologic, the principle that every organ- 

 ism, in its ontogeny, goes through a series of stages, 

 each of which represents a stage in the evolution of 

 that class of organisms to which it belongs ; heredity 

 influencing or securing its palingeny, and the environ- 

 ment causing its kenogeny ; in other words, " that the 

 ontogeny is a short repetition of the phylogeny. " 

 L., Henry's. See Z., Dalton's. L., Hilton's, 

 that a nerve-trunk supplying a given joint also supplies 

 the muscles moving that joint and the skin over the 

 insertion of those muscles. L. of Homotopic 

 Transmission, variations or acquired characters ap- 

 pear in the parts of an individual as in those of its pro- 



genitor. L., Hook and Gravesande' s, of Elasticity, 



that the tension is directly proportionate to the length 

 of the body extended , and to the amount of the extend- 

 ing weights, and that it is also inversely proportionate 

 to the diameter of the extended body. L., Huxley's, 

 the physical differences between man and the higher 

 apes are less marked than those between the higher 

 and the lower apes. L., Joule's, the heating-power 

 of a current is proportional to the product of the resist- 

 ance, the square of the current-strength, and the time the 

 current flows. L., Kirchhoff's, in electricity : 1. The 

 sum of all the positive currents is equal to the sum of all 

 the negative currents, and, hence, if we add these, the 

 result is zero. 2. The sum of all the electromotive 

 forces in any circuit is equal to the sum of all the 

 products obtained by multiplying the separate currents 

 by the resistances through which they are flowing. 

 3. In optics, the law that a transparent body absorbs 

 from a beam of light passing through it those rays which 

 it emits in the incandescent state. See L., Angstrom's. 

 L., Kofacker-Sadler's, a law as to the cause of the 

 difference of sex. From a study of 80,000 cases these 

 observers conclude that if the husband is younger than 

 the wife there ar,e as many boys as girls ; if both are of 

 the same age there are 1029 boys to 1000 girls ; if the 

 husband is older, 1057 boys to 1000 girls. L., Kopp's 

 (of boiling-points), the addition of CH 2 to members of 

 certain homologous series of chemic compounds 

 raises the boiling-point about 19. 5 C. L., Lenz's, 

 the law in electro-magnetic induction that the direction 

 of induced currents is such that their reaction arrests 

 the motion that produces them. L., Levert's, that 

 in placenta praevia there is a marginal insertion of the 

 cord. L., Listing's, pertains to the movements of the 

 eye-ball : when moved from the position of rest, the 

 angle of rotation in the second position is the same as 

 if the eye were turned about a fixed axis perpendicular 

 to the first and second positions of the visual line. 

 L., Louis', in adults the lungs usually contain 

 tubercle when it is present elsewhere in the body. L., 

 Magnus's, in thermo-electricity, the law that " in cir- 

 cuits of the same metal throughout, no electromotive 

 force is produced by variation in temperature or ol 

 section of the conductor at different parts of the circuit.'' 

 L., Malaguti's, when two salts are mixed in solution 

 double decomposition occurs and four salts are formed 

 (metathesis), the proportions of each depending on the 

 strength of union of the respective basic and add 

 radicles. L., Mariotte's, the law of physics that 

 the volume of a gas varies inversely as the pressure to 

 which it is subjected. See L., Boyle's. L. of 

 Molecular Weights, the molecular weight of an 

 element is twice its atomic weight (with the exception 

 of Hg and Cd) ; the molecular weight of a compound is 

 equal to half the sum of the atomic weights ol its 

 elements. L. of Multiple Proportions, that two 

 substances uniting to form a series of chemic com- 

 pounds, do so in proportions that are simple multiples 

 of one another or of one common proportion. L., 

 Newton's, the unit force is that force which, acting 

 for unit time on the unit mass, produces unit \ 

 L., Ohm's, the law that the current-strength varies 

 directly as the electromotive force, and invers< 

 resistance. It is usually expressed by the formula 



C= „ , in which C is the current in ami > 



R + y 

 the electromotive force in volts; R, the resistai 

 the external, and y, that of the internal part of tin- 

 circuit, in ohms. L. of Organic Balance, 

 sive development of one part of an organism is 

 terbalanced by deficient growth of another pai 

 Pfliiger's, "a given tract of nerve is stimulated bj 



