NATURAL PHILOSOPHY. 165 



heat of a body are duo to differences in the amount of heat consumed 

 in molecular work against cohesion or other forces binding the mole- 

 cules together. Or, in other words, to produce in a body no other 

 effect than a given rise of temperature requires the same amount of 

 force, whatever may be the physical condition of the body. Whether 

 the body be in the solid, the fluid, or the gaseous condition, the same 

 rise of temperature always indicates the same quantity of force con- 

 sumed in the simple production of the rise. Now if heat-vibrations 

 consist in excursions of the atom to and fro across a center of equi- 

 librium external to itself, as is generally supposed, then the real 

 specific heat of a solid body, for example, owjht to decrease with the 

 hardness of the body, because an increase in the strength of the force 

 binding the molecules together, would in such a case tend to favor 

 the rise in the rapidity of the vibrations. 



These conclusions not only afford us an insight into the hidden 

 nature of heat- vibrations, but they also appear to cast some light on 

 the physical constitution of the atom itself. They seem to lead to 

 the conclusion that the ultimate atom itself is essentially elastic. 

 For if heat-vibrations do not consist in excursions of the atom, then 

 it must consist in alternate expansions and contractions of the atom 

 itself. This again is opposed to the ordinary idea that the atom is 

 essentially solid and impenetrable ; but it favors the modern idea that 

 matter consists of a force of resistance acting from a center. 



EFFECT OF THE COLLISION OF THE MOON AND THE EARTH. 



If we imagine the moon in the course of time, either in conse- 

 quence of the action of a resisting medium, or from some other cause, 

 to unite herself with our earth, two principal effects are to be dis- 

 cerned. A result of the collision would be, that the whole mass of 

 the moon and the cold crust of the earth would be raised some thou- 

 sands of degrees in temperature, and consequently the surface of the 

 earth would be converted into a fiery ocean. At the same time, the 

 velocity of the earth's axial rotation would be somewhat accelerated, 

 and the position of its axis with regard to the heavens, and to its own 

 surface, slightly altered. If the earth had been a cold body without 

 axial rotation, the process of its combining with the moon would have 

 imparted to it both heat and rotation. It is probable that such pro- 

 cesses of combination between different parts of our' globe may have 

 repeatedly happened before the earth attained its present magnitude, 

 and that luxuriant vegetation may have at different times been buried 

 under the fiery debris resulting from the conflict of its now component 

 masses. JR. Mayer, Sillimaii's Journal. 



THE DISCRIMINATION OF ORGANIC BODIES BY OPTICAL 



PROPERTIES. 



Prof. G. G. Stokes recently delivered a lecture before the Royal 

 Society "On the discrimination of organic bodies by their optical 

 properties," especially by means of the apparatus of Kichhoff and 

 Bunsen, whereby the spectrum of any substance may be produced 

 with the greatest facility, thus affording a test for the presence of 

 certain substances in compounds, showing their chemical identity, &c. 

 By means of the electric lamp and the large apparatus of the society 



