Theory 



SCIENTIFIC SIDE-LIGHTS 



tion of such an interpenetration of theo- 

 retical knowledge and experimental skill. 

 HELMHOLTZ Popular Lectures, lect. 1, p. 19. 

 (L. G. & Co., 1898.) 



34O3. THEORY OF CREATION 



Sketch of the Nebular Hypothesis. In their 

 view [i. e., the view of Kant and Laplace, 

 known as " the nebular hypothesis "] our 

 system was originally a chaotic ball of nebu- 

 lous matter, of which originally, when it 

 extended to the path of the most distant 

 planet, many billions of cubic miles could 

 contain scarcely a gram of mass. This 

 ball, when it had become detached from the 

 nebulous balls of the adjacent fixed stars, 

 possessed a slow movement of rotation. It 

 became condensed under the influence of 

 the reciprocal attraction of its parts; and, 

 in the degree in which it condensed, the 

 rotatory motion increased, and formed it 

 into a flat disk. From time to time masses 

 at the circumference of this disk became 

 detached under the influence of the increas- 

 ing centrifugal force; that which became 

 detached formed again into a rotating nebu- 

 lous mass, which either simply condensed 

 and formed a planet, or during this con- 

 densation again repelled masses from the 

 periphery, which became satellites, or in 

 one case, that of Saturn, remained as a 

 coherent ring. In another case the mass 

 which separated from the outside of the 

 chief ball divided into many parts, detached 

 from each other, and furnished the swarms 

 of small planets between Mars and Jupiter. 

 HELMHOLTZ Popular Lectures, lect. 4, p. 

 173. (L. G. & Co., 1898.) 



34O4. THEORY OF "CRYSTAL 



SPHERES" The Conception of the Middle 

 Ages Destruction of Theory by Kepler. 

 The idea of a crystalline vault of heaven 

 was handed down to the Middle Ages by the 

 fathers of the church, who believed the fir- 

 mament to consist of from seven to ten 

 glassy strata, incasing one another like the 

 different coatings of an onion. This sup- 

 position still keeps its ground in some of 

 the monasteries of Southern Europe, where 

 I was greatly surprised to hear a venerable 

 prelate express an opinion in reference to 

 the fall of aerolites at Aigle, which at that 

 time formed a subject of considerable in- 

 terest, that the bodies we called meteoric 

 stones with vitrified crusts were not portions 

 of the fallen stone itself, but simply frag- 

 ments of the crystal vault shattered by it in 

 its fall. Kepler, from his considerations of 

 comets which intersect the orbits of all the 

 planets, boasted, nearly two hundred and 

 fifty years ago, that he had destroyed the 

 seventy-seven concentric spheres of the cele- 

 brated Girolamo Fracastoro, as well as all 

 the more ancient retrograde epicycles. 

 HUMBOLDT Cosmos, vol. iii, p. 125. (H.", 1897.) 



34O5. The System of 



Pythagoras " Music of the Spheres." He 

 [Pythagoras] is said to have taught that 

 the heavenly bodies were set in a number 



of crystalline spheres, in the common center 

 of which the earth was placed. In the outer 

 of these spheres were set the thousands of 

 fixed stars which stud the firmament, while 

 each of the seven planets had its own sphere. 

 The transparency of each crystal sphere was 

 perfect, so that the bodies set in each of 

 the outer spheres were visible through all 

 the inner ones. These spheres all rolled 

 round on each other in a daily revolution, 

 thus causing the rising and setting of the 

 heavenly bodies. This rolling of the spheres 

 on each other made a celestial music, the 

 " music of the spheres," which filled the fir- 

 mament, but was of too elevated a char- 

 acter to be heard by the ears of mortals. 

 NEWCOMB Popular Astronomy, pt. i, int., p. 

 3. (H., 1899.) 



34O6. THEORY OF DEW An Effect 

 of Chilling by Radiation. A series of ex- 

 periments, conceived and executed with ad- 

 mirable clearness and skill, enabled Dr. 

 Wells to propound a theory of dew, which 

 has stood the test of all subsequent criti- 

 cism, and is now universally accepted. It 

 is an effect of chilling by radiation. " The 

 upper parts of the grass radiate their heat 

 into regions of empty space, which, conse- 

 quently, send no heat back in return; its 

 lower parts, from the smallness of their 

 conducting power, transmit little of the 

 earth's heat to the upper parts, which, at 

 the same time, receiving only a small quan- 

 tity from the atmosphere, and none from 

 any other lateral body, must remain colder 

 than the air, and condense into dew its wa- 

 tery vapor, if this be sufficiently abundant 

 in respect to the decreased temperature of 

 the grass." Why the vapor itself, being a 

 powerful radiant, is not so quickly chilled 

 as the grass, has been already explained 

 on the ground that the vapor has not only 

 its own heat to discharge, but also that of 

 the large mass of air by which it is sur- 

 rounded. Dew, then, is the result of the 

 condensation of atmospheric vapor, on sub- 

 stances which have been sufficiently cooled 

 by radiation; and as bodies differ widely in 

 their radiative powers, we may expect cor- 

 responding differences in the deposition of 

 dew. This Wells proved to be the case. He 

 often saw dew copiously deposited on grass 

 and painted wood, when none could be ob- 

 served on gravel walks adjacent. TYNDALL 

 Heat a Mode of Motion, lect. 17, p. 498. 

 (A., 1900.) 



34O7. THEORY OF "FACULTIES" 

 A BONDAGE Feeling, Desire, Impulse, and 

 Will Combine in Free Choice. It is in the 

 doctrine of feeling and will more than any- 

 where else that psychology still wears the fet- 

 ters of the old faculty theory. . . . Thus first 

 of all feeling was considered apart from its 

 connection with will, and then desire was 

 treated as a separate process, sometimes 

 found in connection with feeling. Further, 

 impulse was opposed to desire proper as an 

 obscure desire, in which the subject is not 



