544 



PHYSICS, PROGRESS OF, IN 1902. 



contraction to one-eighth of its volume, with cor- 

 responding increase of pressure, will initiate a loss 

 of heat by radiation, while the mass continues to 

 rise in temperature. If the pressure increases 

 more rapidly than in the ratio of 16 to 1, a second 

 stage will be reached in which the mass will be 

 cooled by contraction. With hydrogen and nitro- 

 gen, Amagat has shown that this will occur (at 

 pressures of more than 250 to 300 atmospheres) at 

 about 17 C. The densities of the nebulae are 

 much less than this, so that if they lose heat by 

 radiation, their temperatures will increase more 

 rapidly, and therefore, conversely, the communi- 

 cation' of heat from outside will cause cooling ac- 

 companied by expansion. This expansion would 

 continue indefinitely if it were not for comets and 

 meteorites. When new stars begin to form a solid 

 crust, the loss of energy will fall suddenly, and 

 this third stage will therefore continue indefinite- 

 ly. With bodies in the second and third stages 

 collisions will give rise to explosive outbursts of 

 gases, and these would form spiral nebulas. The 

 author points out that there will be practically no 

 dissipation of gravitational energy during expan- 

 sion, and none through ordinary chemical dissocia- 

 tion. There will be dissipation, however, .in photo- 

 chemical processes inverse to those which occur 

 on the surface of the earth, and the series of 

 changes may go on without intermission. The 

 average period of the cyclical changes is on the 

 increase, so that the quantity of nebulous mate- 

 rial in existence must continually become greater, 

 while that of the stars must correspondingly de- 

 creaae. 



Properties of Matter, etc. Gravitation. 

 V. Wellman (Astrophysical Journal, May) at- 

 tempts to explain the Newtonian law of gravita- 

 tion by supposing a gaseous ether of extreme 

 tenuity, whose particles possess velocities ap- 

 proaching that of light. On this supposition grav- 

 itation must be modified if the attracting masses 

 are in relative motion. The modifying factor 

 involves the velocity of the ether particles, which 

 the author assumes to be equal to that of 

 light in racuo. The resulting " gravitation fac- 

 tor " agrees with the constant of Gauss so closely 

 that " a merely accidental coincidence of the two 

 values is out of the question, and a causal con- 

 nection between light and gravitation seems to be 

 expressed in the figures." The distribution of 

 what he calls " gravitational matter " is dis- 

 cussed by Lord Kelvin in a British Associa- 

 tion paper (Nature, Oct. 24, 1901). Ether, 

 according to Lord Kelvin, is matter, but not 

 gravitational matter, because if it- gravitates it 

 must be infinitely incompressible, which to the 

 author appears improbable. It is assumed that 

 the Newtonian law of attraction between 

 masses of gravitational matter holds through- 

 out infinite interstellar space. The author 

 considers it probable that there may be as much 

 matter as a thousand million suns within a sphere 

 of radius 3.09 X 10" kilometers (the distance at 

 which a star's parallax is 0.001 of a second), be- 

 cause, if uniformly distributed at rest throughout 

 such a space, twenty-five million years ago, they 

 would now have acquired, by mutual attraction, 

 velocities comparable to the present velocities of 

 the stars. Kelvin also states that if all the matter 

 in the universe were, at a certain epoch, at rest, 

 and unequally distributed, there would be a tend- 

 ency for the densities to become more unequal, 

 solid bodies would ultimately form, and there 

 would be collisions, giving rise to waves in ether, 

 carrying energy away to infinite space. The ori- 

 gin of meteoric stones is attributed to this kind of 

 cooling. 



The Ether. Hopkinson (Philosophical Mag- 

 azine, January) argues that optical and other 

 terrestrial phenomena, including gravity, fail, with 

 one exception, to give any logical non-metaphys- 

 ical basis for postulating the existence of an ether. 

 This one exception is the fact that, according to 

 the undulatory theory, the aberration of a star 

 depends on the motion of the earth relative to the 

 free ether, and is entirely unaffected by the motion 

 of the star, which, if capable of experimental 

 proof, would give such a logical basis. Certain 

 stars, the so-called " spectroscopic binaries," appear 

 single when viewed through a telescope, but are 

 inferred to consist of two components because of 

 the periodic doubling of lines in their spectra. 

 This would occur, owing to the Doppler effect, 

 when one component of the system is moving to- 

 ward, and the other away from, the earth. If 

 the motion of the components affected their aber- 

 ration, then, when moving as above, there should 

 be a lateral separation between the components as 

 seen in a telescope, resulting in a periodic dou- 

 bling alternating with the separation of the spec- 

 troscopic lines. The fact that no such doubling 

 can be detected affords, in the author's opinion, 

 evidence that the aberration is unaffected by the 

 motion of the star, and gives a logical basis for 

 postulating an ether. 



Molecular Fields of Force. S. Leduc (Comptes 

 Rendus, Feb. 17) has attempted to explain a 

 number of phenomena by applying the notion of 

 fields of force to molecular movements in liquids. 

 When a drop of any aqueous solution falls into 

 distilled water the dissolved molecules diffuse in 

 all directions and water moves in an opposite di- 

 rection to replace them. The drop is then the 

 seat of a field of force, the directions followed by 

 the moving molecules being the force lines. A 

 similar but inverse field is established when a crys- 

 tal forms in a solution. By retarding the molecu- 

 lar movements by a colloid such as gelatin, and 

 drying the liquids rapidly, photographs of the 

 molecular fields of force have been obtained, ex- 

 hibiting also interference between fields of force 

 of diffusion, or between fields of force of diffusion 

 and crystallization. 



Mechanics. Pressure of Vibrations. Lord 

 Rayleigh (Philosophical Magazine, March) gives 

 several examples to show how the energy of a 

 vibrating system may be drawn off and converted 

 into other forms of work. In one of these, a 

 string is attached at its upper end to a vertical 

 axis, and ft ring slides over the axis, including 

 the upper part of the string, the lower part being 

 free. To the lower end is attached a pendulum, 

 which, when set swinging, tends to force the ring 

 upward, any work done in raising it being at 

 the expense of the vibration energy. By mathe- 

 matical calculation it may be found that raising 

 the ring to an infinite distance would exhaust the 

 whole energy of vibration. The author raises the 

 question whether an analogue of the second law 

 of thermodynamics can be found in the general 

 theory of the pressure of vibrations, but does not 

 give, apparently, a final answer. 



Measurement of Minute Masses. E. Salvioni 

 (Nuovo Cimento, May) has devised a microbal- 

 ance, made of a thin thread or ribbon of glass or 

 other material, fixed at one end. The device is 

 placed in a closed case, which also contains small 

 weights (the larger of platinum wire, the smaller 

 of silk thread), which can be placed on the flexible 

 thread or ribbon. The bending of the loaded 

 thread is observed with a micrometer, and appears 

 to be proportional to the weight. A glass thread 

 10 centimeters long and one- to two-tenths of a 

 millimeter in diameter will thus support a weight 



