260 M. Ramond's Inslructiom for the Application of [Oct. 



sides by very high mountains. I have always found the result 

 too little. 1 have since tried to measure the height of the Pic 

 de Midi above Bareges : I am now at the thirty-second trial, 

 and the measurement is always found too great. These two 

 observations, one of which is, as it were, the complement of the 

 other, have concurred most conclusively to persuade me that 

 there really exists in deep valleys a constant compression of the 

 atmosphere, the effect of which is to augment the height of the 

 mercurial column. 



I recommend it as highly desirable to repeat observations 

 with care, and on a large scale, in order to examine more closely 

 the decrease of heat and moisture, and the action of ascending 

 and descending currents. Three or four barometers disposed at 

 different intervals of height, might teach us much, and give an 

 unexpected turn to some inquiries ; but the differences of eleva- 

 tion must be great ; and above all, the stations must be very 

 favourable. To dispose the instruments in this way on the side 

 of a high mountain would, perhaps, be the first expedient we 

 should be led to think of, but assuredly the last to which I 

 would have recourse. Nothing is certain on long acclivities, 

 where the heat of the ground and the inclination of the currents 

 modify in a thousand ways the pressure of the atmosphere and 

 its temperature. We cannot be too careful in discarding from 

 delicate observations even the most distant suspicion of those 

 local perturbations, of which we cannot exactly estimate the 

 amount. The stations to be preferred are eminences well 

 exposed to the air; summits near others, but to a certain point 

 independent ; plains of some extent ; but no narrow gorges ; no 



Seaks greatly above others; and after my experiments at 

 lareges, I would not place my barometer in a narrow valley, 

 even if I should be reduced to the necessity of seeking a more 

 convenient station at some distance ; for the distance has a 

 much less influence on the accuracy of the measurements than 

 the favourable or unfavourable configuration of the places where 

 the instruments are situated. 



Barometrical measurements would inspire less distrust if the 

 observations had been always made with the precautions which 

 the nature of the operation indicates ; and there would not be 

 so much dispute on the value of the coefficients and the princi- 

 ples of our formiilaj, if the disagreements were not in a great 

 measure produced by the confidence which is too often reposed 

 in observations in themselves very defective. In the present 

 Btate of the science, it would be much better to endeavour to 

 bring to perfection the very difficult art of observing : to study 

 the circumstances which are favourable, to examine and point 

 out the sources of error ; to multiply trials with that patience 

 which the minutest precautions will not tire ; with that honesty 

 which will not evade difficulties ; with that discernment which 

 directs a depth of study proportioned to the difficulties attach- 



