TIDES. 



Zl 



higher than the solar. It may appear a matter of surprise that the 

 sun, which attracts the earth with a force amazingly more powerful 

 than that exerted by the moon, should produce a feebler tide. But 

 the reason of this will be apparent when the cause of the tides is 

 understood ; it will be then seen that it results from the proximity of 

 the moon. 



Let us first inquire into the cause of the solar tide. The sun 



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attracts the earth with that force which prevents the earth from 

 maintaining a straight course ; which bends its path into the vast 

 eclipse that the earth sweeps out round the sun every year. It will 

 be convenient in the first stage of our inquiry to leave out of con- 

 sideration the daily rotation of the earth on its axis. Let then the 

 dotted hnes of the figure (Fig. 5) represent portions of the annual paths 

 which would be pursued by the points o, b, and d, if we suppose 

 that, instead of a daily rotation, b is kept always turned towards the 

 sun. These orbits would be all of them traversed in the same period, 

 viz., a year ; and they differ slightly in size, the orbit of which d z is 

 a portion being the largest, while a x is the smallest, and B y of 

 intermediate size. Now, when orbits of dift'erent sizes are thus 



D 



