742 THE EIFFEL TOWER. 



from high points of laud or from vast structures of masonrj', which re- 

 tain much heat, causing currents of air that interfere with observations 

 or make them inexact. The variability of rain-fall could be well ob- 

 served, also the average height to which fogs reach above the earth's 

 surface near Paris. A relatively complete knowledge might be gained 

 of the volume of water held in different air strata. This would make 

 clear the reason why clouds light in volume sometimes precipitate so 

 much water. As the condition of the air varies with the height, the 

 advantage of having instruments far enough apart, one above the 

 other, is obvious. On calm days, the general direction of the wind 

 would be free from the effect of local heat accumulation due to the in- 

 fluence of neighboring buildings. All these phenomena could be care- 

 fully observed at a height to which only balloons ascend for an appre- 

 ciable length of time. At this distance from the ground, the atmos- 

 pheric conditions, freed from the surroundings of a mountainous or 

 hilly region, are not precisely known. 



A position above tlie fogs that very often obscure the horizon of Paris 

 will facilitate astronomical observations impossible in ordinary weather. 

 The vibration of the tower will doubtless exclude it from use in obtain- 

 ing the precise positions of the stars, as pointed out hy some astrono- 

 mers, but it will leave the field free to researches regarding the chemi- 

 cal constituents of the stellar universe. Observations intended to es- 

 tablish the proper motions of stars by the displacement of lines in the 

 spectrum would be more exact at a height of 1,000 feet than at that of 

 the observatories. Photographic apparatus at the summit of the tower 

 would be mor^ efficient in case of an eclipse near the horizon, but work 

 upon stars or nebulae, requiring steadiness of position, ought to be re- 

 served for calm nights. In ever3^ case the moon and the planets could 

 be studied and drawn under more favorable conditions. The known 

 temperature of the air at diiierent heights is also of great importance 

 in astronomical observations, because the resulting variation in refrac- 

 tion is so often a matter of conjecture. 



In addition to the above experiments in meteorology, electrical science, 

 and astronomy, there remain to be considered further questions of vege- 

 table chemistry, peculiarities of growth under various conditions, and 

 more exact data respecting the material constituents floating in the air. 

 Further and finer investigations can be made, showing with additional 

 interest the value of Foucault's well-known pendulum experiment de- 

 monstrating the rotation of the earth. The possible relation between 

 magnetism and gravitation, which Faraday investigated with a falling 

 body, might be carried further with advantage. 



The instantaneous transmission of time signals for the benefit of all 

 Paris, the more exact measurement of the velocity of sound under 

 various atmospheric conditions, the estimated resistance of the air as a 

 body falls at given rates of speed, the law of metallic elasticity, in the 

 contraction and expansion of the iron-work of the structure, the study 



