20 NATURE-STUDY REVIEW [17:1— Jan., 1921 



averag^e time between two tides is about twelve hours and twenty- 

 five minutes and each day the tide is about fifty minutes later 

 than it was the day before owing to the fact that the moon rises 

 that much later each day. Each tide consists of two phases, high 

 tide and low tide; a tide consists of a wave moving from east to 

 west ; this wave is about three feet in height on the ocean but as it 

 moves up against the land, it may heap up until, as in the Bay of 

 Fundy, it is sixty feet or more in height. On Long Island the tide 

 is not more than three feet high while on the coast of Maine it 

 averages ten to twelve feet. 



Every lunar month there are two great tides called spring tides 

 and two small tides known as neap tides. The spring tide 

 when the moon is new, that is when it is on the same side of the 

 earth as the sun and the two act together, the sun and moon pulling 

 in a straight line and therefore raising a higher tide. The neap 

 tides occur when the moon is on its first and third quarters, for 

 then the sun and rrioon are pulling the earth in different direc- 

 tions. 



The moon does us great sendee in sanitation ; the tides prevent 

 the stagnation of water at the mouths of rivers which carry away 

 the filth and waste matter from cities and great areas of populated 

 lands. They wash up into the rivers and then retreat carrying 

 with them out to sea great burdens of matter that would breed 

 pestilence if not removed. Somebody has very cleverly said "the 

 tide is a toothbrush and antiseptic wash for the mouth of a river." 



The Measurement of Betelgeuse 



Professor Albert A. Michelson, the famous physicist, has devised 

 a means of measuring stars, and has just announced the size of 

 Alpha Orionis, better known as Betelgeuse, the red star in the 

 shoulder of Orion. The result is too stupendous for oiir compre- 

 hension, for the diameter of this star is 260,000,000 miles and its 

 voliime is 37,000,000 times as great as our sun; in the place of our 

 sun this great fiery ball would reach almost to the orbit of Mars. 

 The light reaching our eyes now from Betelgeuse started on its 

 journey before our Revolutionary war was fought, for it takes 150 

 years for light to reach us from it. 



