LAPLACE AND AMPfeRE 223 



velocity of sound is influenced by the heat phenomena which 

 are necessarily always an accompaniment of the sound 

 waves. Dalton had already showed that air becomes heated 

 when compressed, and cooled when expanded, and Gay- 

 Lussac made the first measurements of this phenomenon. 

 But pressure changes of this kind take place in all sound 

 waves, and the temperature changes connected therewith 

 cannot be without influence on the velocity of propagation, 

 for they influence the elastic forces of the air. Laplace 

 calculated this influence, using as his basis Newton's first cal- 

 culation of sound velocity, and found that we need to add to 

 Newton's formula the ratio of the two specific heats of air 

 (at constant pressure and constant volume) under the square 

 root sign. The more accurate determinations of the velocity 

 of sound then available already demanded such an increase as 

 compared with Newton's formula, and the refined measure- 

 ments of the ratio of the two specific heats which were then 

 undertaken - on the basis of a sharp definition first given 

 by Laplace in this connection - showed full agreement 

 between Laplace's calculation and hence the idea upon 

 which it was based, and reality. 



Ampere was born in Lyons, where his father was a well- 

 to-do merchant. He early showed extraordinary mathe- 

 matical ability, but in other respects also a wide range of 

 mental activity. He was brought up alone in the country, 

 to which his father had retired, and his studies were accom- 

 plished, with a little assistance from his father, by means of 

 books. At this time of many sided education and growing 

 personality, at the age of eighteen years, he had the mis- 

 fortune to be cruelly robbed of his father, who was declared 

 to be an aristocrat, and became a victim of the mass-murder 

 of the Revolution. For over a year he wandered about 

 distracted and planless, until he was seized for the moment 

 by an especial interest in botany, one of the many studies 



