SCIENCE LETTER FROM PARIS. 045 
placed in line, would extend to an inch. Molecules are very elastic, and when 
unopposed by obstacles, move rapidly and in aright line ; when they move freely, 
they represent the w/tra gaseous state of matter, as obtained by Crookes in almost 
a vacuum; when they knock against each other, following the law of elastic 
bodies, thus putting an obstacle reciprocally to their own movement—gas is the 
result ; when the field of the movement of the atoms is restrained, but not wholly 
stopped, a /zguzd is the product, and when the attraction is sufficient to produce 
cohesion, to keep the molecules confined to their proper sphere, that state of 
matter is called sold. All that changes the movement of matter, or the mole- 
cules which compose it, is a form of force: Thus weight, attracting matter to the 
center of the globe, is a form of force; so is heat, for it determines in the 
molecules of matter violent vibrations, or augments the rapidity of their move- 
ments in a right line—that which products the measure of heat, called—tempera- 
ture. Light is also a form of force, being the product of the undulations of the 
molecules of matter, transmitted by the undulations of that mzliew which fills all 
space—ether. No person has ever seen a molecule, and the mind’s eye can 
form no idea of force. All that is mysterious and incomprehensible in nature is 
attributed to things not less mysterious and also as incomprehensible. This has 
ever been the case with such phenomena as life, heat, magnetism and electricity. 
For the Greeks, heat was an animal which bit, later it was accepted asa fluid, 
which permeated and inflamed bodies, till Rumford demonstrated it was merely 
a movement, and Joule a quantitative form of energy. Thalesand Milet imagined 
‘the lodestone was endowed with a sort of immaterial spirit, and the Greeks con- 
cluded amber was possessed of vitality because it attracted morsels of straw. 
Boyle held that amber emitted a kind of glutinous fluid which carried off light 
objects by attracting them toward the excited body. Du Fay imagined the 
theory of two fluids, Franklin of one, and that Cavendish completed, but it was 
Faraday who discovered the molecular theory of electricity, and Grove ranked it 
with light and heat as being a force of the same nature and simply a mode of 
movement. Deprived of dimension, inertia and elasticity, electricity cannot be 
a form of matter; consequently it is a form of force lke sound, light and heat. 
‘The analogy between the conductibility of the different metals for heat and 
electricity is such, that were th€ metals pure, their manner of conductibility 
would be the same. When an electric current passes through a metallic wire, it 
heats the metal, and to a degree proportionate to the intensity of the current, till 
the wire becomes incandescent. All electric discharge is but a violent molecular 
movement, and this view is corroborated by the fact, that in vacuum, the dis- 
charge cannot take place. M. Plouké has shown that fine wires, traversed by 
powerful currents, present regular ripples, some peculiar crackings, causing the 
‘metal to become peculiarly brittle; hence, the vibratory movement of the 
molecules. M. Siemens calculates that New York could be illuminated by the 
force of the water falling at Niagara, and that a plow could be worked—the writer 
hhas seen such on the estate of M. Menier, as well as cranes worked for unloading 
