Fig. 1. PROCESS OF MAKING A BAUOMKTEK. 



THE BAROMETER. 



1. Origin of the name. 2. Conditions necessary to render the instrument 

 useful. 3. To purify the mercury. 4. To cleanse the tube. 5. To 

 fill the tube. 6. To invert it in the cistern. 7. Construction of a 

 barometer. 8. Effect of temperature on the barometric column. 9. To 

 ascertain if the vacuum above the column be perfect. 10. Expedients 

 to render minute variations of altitude visible. 11. Diagonal 

 barometer. 12. Wheel barometer. 13. Common siphon barometer. 

 14. Use of the barometer to measure heights. 15. Density of 

 strata affected by their temperature. 16. Fall of barometer in the 

 balloon ascent of Gay Lussac. 17. Extreme variations of the 

 barometric column in a given place. 18. Its diurnal variation. 

 19. How it may prognosticate the weather. 20. Fallacy of popular 

 rules. 21. Barometric prognostics. 



LARDNER'S MUSEUM OF SCIENCE. 

 No. 44. 



177 



