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notice that the unusual duration of the eclipse of August17th, 1868, in the neighbourhood of the Gulf of Siam (iuwhich locality, as we have previously stated, it lasted for nearlyseven minutes), was to a very appreciable extent thus produced,owing to the Moon and Sun being nearly in the zenith, or,popularly speaking, overhead, at the time of its occurrence.
Our space forbids that we should refer, otherwise than verybriefly, to the benefits which the Earth derives from theinfluence of the Moon upon its waters. For the same reasonwe must refrain from discussing the somewhat complicateddynamical investigations involved in a proper explanationof the origin of the Tides. * But we may very positively affirmthat if the tidal disturbance of our seas and rivers were tocease ; if they were to become stagnant, except so far as oceancurrents and rainfall might affect them ; most disastrous con-sequences both to health and commerce would ensue.
We can hardly over-estimate the vast benefit which theunceasing power of the tides confers, in sweeping awaydeleterious matter, iu raising vessels into locks and harbours,in bringing merchandize up our great rivers, and in manyother ways. It may also be that, some day, much of theimmense energy provided by them, which is still unused,will be applied to drive machinery, or to compress air, or togenerate electricity, which being economically carried to dis-tant points of application, may be utilized to an extent atpresent little imagined.
Were it only for the beneficial influence of the tides, wemight well be very thankful that the Earth possesses soinfluential a satellite. And this feeling is increased, when webear in mind, that the knowledge of the Greenwich time atwhich the Moon is seen at a certain apparent distance from
* For a most lucid and interesting description of Mr. G. H. Darwin’stheory of tidal evolution, affording reasons for believing that millionsof years ago tides of much greater dimensions than those of the presenttime may have swept across the Earth ; as well as for an explanation ofthe connection between the Moon ’s distance, the tides, and the graduallengthening of the Earth ’s day, we refer our readers to Dr. Ball’s learnedand eloquent lecture recently published by Messrs. Macmillan and Co.,and entitled “A Glimpse through the Corridors of Time."