44 CHEMISTRY AND PHYSICS IN RELATION 



difference arises from the specific heat of the air from the amount of heat which, 

 on the propagation of* the sound, is liberated from the molecules of air set in mo- 

 tion. It is clear that this difference in the velocity of propagating sound in other 

 gases, which, with equal volumes, contain and give out on pressure, more or less 

 heat than the air, must be greater or less than that of the atmosphere ; and it is, 

 therefore, easy to perceive how the numbers, which express these unequal velocities 

 in the propagation of sound in different gases, afford us at the same time a standard 

 by which to measure the unequal quantity of heat which they contain. 



As now the height or depth of the tone depends upon the number of vibrations 

 of a sound-wave in a second, that is, upon the velocity with which a motion once 

 impressed propagates itself, and we know that in all gases the velocity of the pro- 

 pagation of a sound-wave is directly proportionate to the number of vibrations of 

 the tones that are called forth thereby, we perceive how, by the unequal height 

 of the tone which is brought out by means of a pipe from different gases (that is 

 by ascertaining how much more one gas contains than another), we are able to find 

 the specific heat of the gas. Acoustics owe the rank they hold at the present time 

 to the great discovery, that musical harmony each tone that touches the heart, 

 attuning it to joy, or animating it to courage is the symptom of a definite and de- 

 finable number of oscillations of the molecules of the propagating medium, and a 

 sign of all that can be determined according to the laws of undulations of this 

 motion. A number of facts referring to tones might be drawn from the theory of 

 undulation, while empirical truths have led to a corresponding knowledge of the 

 properties of vibrating bodies, which were previously quite unknown. 



It is asserted of a celebrated Viennese violin maker, that he was accustomed to 

 select the wood for his violins, by making choice of those trees, which, on his 

 striking them with a hammer, returned a certain sound, known to himself alone. 

 This may be a mere fable ; but there can be no doubt, that he knew the importance 

 of selecting boards for the upper and lower parts of his instruments, which should 

 make the same number of oscillations in a second, and that this property depended 

 upon the thickness of the boards used. 



ELECTRICITY AND MAGNETISM, MAGNETISM AND HEAT, 

 MAGNETISM AND CHEMICAL FORCE. 



If, finally, we consider that the electrical current passing through a metal wire 

 stands in a peculiar relation to the magnetic properties which it receives ; and if 

 we remember that, by the magnetic needle the minutest differences of radiated heat 

 may be detected, that the quantity of electricity in motion is expressible in numbers 

 by means of the same electrical needle, and can be measured in cubic inches of 

 hydrogen, and, by metalic weights ; and that, finally, when we see how the 

 causes or forces, from which the properties of bodies and their capacities to make 

 an impression upon our senses stand in a relation of mutual dependence to each 

 other, we cannot doubt that the vital properties are equally dependent with all 

 others, upon these laws, and that the chemical and physical properties of the 

 elements, with their form and method of arrangement, play an appreciated and 

 appreciable part amongst the phenomena of life. 



VITAL PROPERTIES ARE NO EXCEPTION TO A LAW OF NATURE. 



It doubtless arises from the method they have adopted, that many physiologists 

 and pathologists are led to look upon vital properties as in some degree exceptions 

 to a great natural law ; for how else can we explain the fact of their not regarding 

 the number and grouping of those elements from which the parts of the organism 

 have been composed as a physical property affording indispensable assistance to- 

 wards the attainment of an insight into vital phenomena ; how else can we explain 

 their not taking into account, in the treatment of disease, the elementary composi- 

 tion of the means of cure, and the properties depending upon them, on which their 

 action rests. The mere knowledge of a formula is not of course sufficient for 



