performed ly Messrs. Guy-Liissac and Biot, 375 



found that it would be necessary to watch the transition 

 from the one motion to the other, because in the interval 

 we remained stationary. We took advantage of this re- 

 mark to make our experiments j but, as this stationary state 

 continued only some moments, it was not possible to observe 

 twenty concentric oscillations, as on the earth : we were 

 obliged to be satisfied with five, or at most ten ; taking care 

 not to agitate the car ; for the slightest motion, that even 

 produced when we let the gas escape, or of our hand when 

 we wrote, was sufficient to turn us aside. With all these 

 precautions, which required a great deal of time, we found 

 means to make ten experiments in the course of the voyage, 

 and at different altitudes. The results in the order in which 

 we obtained them were as follow : 



Calculated 



Heights in Number of the Time. 



Alctrcs, Oscillations. Seconds. 



2SQ7 - 5 - - 35 



3088 - - 5 ' - - ( 35 



The same - 5 - - 35 



The same - 5 - - 35 



28o\> 10 * - 70 



3145 - 5 - - 35 



3665 - - 5 - - 35*5 



3589 10 - - 68 



3742 - 5 ^ - 35 



3977 or 2040 toises 10 - - 70 



All these observations, made in a column of more than 

 a thousand metres in height, agree in giving 35 seconds 

 for the duration of five oscillations : but experiments made 

 on the earth give 35^ for this duration. The small difference 

 of a quarter of a second is of little importance^ and at any 

 rate does not tend to indicate a diminution. 



The same may be said of the experiment which gave at 

 one time 68 seconds for 10 oscillations > which makes 34 

 for live : it indicates as little a diminution. It appears to 

 us, therefore, that we may with certainty establish the fol- 

 lowing proposition : 



The magnetic property experiences no appreciable dimi- 

 nution from the surface of the earth to the height of 4000 

 metres. Its action in these limits is constantly manifested 

 by the same effects and according to the same laws. 



It remains for us to explain the difference between these 

 results and those of the philosophers before mentioned. And 



* Voyage dan? les Alpes, tome iv. p. 312, 313. 



C c 2 first, 



