QUERIES AND ANSWERS. 



Readers arc invited to send in Questions ami to ansicer the Onenes icItieJi are printed fu tliis page. 



QUESTIONS. 



Numbers 14. 16. 17. 18. and 20 (Page 461) still remain 

 nnanswered- 



21. ASTRONOMY .WD GKOGK.APHY.— Will any fellow- 

 teacher advise me as to good school experimental and observa- 

 tional courses in astronomj- and geography ? 



Bei.i.krbv Lowkrison. 



22. K.ADIUM. — Seeing that Radium is not a stable 

 substance, but is continually changing with other forms of 

 matter, none of which are stable as far as we know, how is 

 it that Radium is still found in the crust of the earth ': 



J. G. Sparke (Lieut. -Ciilonel). 



23. THE GULF STRE.\M.— .\ friend mentioned the Gulf 

 Stream the other day, and I remarked that I understood that 

 this was now considered to have no effect whatever on Britain. 

 Will you briefly inform me. in "Knowledge." if I am correct, 

 and what are the facts of the case ; how far away is the nearest 

 trace of this stream perceptible, and so on r 



S. P. Rowlands. 



24. DRIi.-\MS. — I should be pleased if some of your readers 

 would give an explanation of the following common occurrence 

 in dreams. Suppose one dreams of an impending railway 

 collision. In the ordinary sequence of events, one dreams of 

 the two trains approaching one another before the actual 

 collision. Now it is a peculiar fact the collision is frequently 

 emphasised in the world of reality b>- a door banging, or some 

 such sudden noise. In fact, one might almost say that every 

 real occurrence impressed on our senses during sleep fits in 

 perfectly with the whole plan of the dream. In the example 

 I have just cited one expects a noise at the moment of the 

 collision, and it happens. If that particular door was not 

 about to slam it is probable, in fact almost certain, that that 

 dream would not ha\e occurred. 



Do you think this any evidence that the mind is often 

 aware of the e\ents of the future : , P ... 



TIDES. — There is a point in connection with the tides of 

 the ocean which I have never seen elucidated in any popular 

 manner. 



Tidal friction causes retardation in the rotation of the earth. 

 and by the principle of conservation of the moment of 

 momentum the revolution of the moon is accelerated. This 

 is the basis of Darwin's theories of tidal evolution, and, of 

 course, remains true whatever may be the lag of the tides 

 behind the moon. The acceleration of the moon is sometimes 

 further explained by a diagram illustrating that the nearer 

 tidal protuberance exerts greater attraction on the moon than 

 the one opposite, much as the precession of the equinoxes is 

 always illustrated. Now the depth of our oceans being less 

 than the critical depth of about fourteen miles, our tides are 

 inverted, that is, high tide where low tide would be expected, 

 and vice-versa : but if the depth were greater than fourteen 

 miles the tides would be direct, and the nearer tidal protu- 

 berance should be behind instead of in front of the moon, and 

 it seems to need popular explanation why a retardation of the 

 lunar revolution does not result. The whole question of the 

 lag of the tides on an ocean-covered earth might receive more 

 notice in popular accounts, though probably too mathematical 



for full elucidation. i n ^ 



J. H. (i. 



REPLIES. 



10. W.\TER .-^ND ITS OWN LEVEL.— I am a little 

 perplexed myself about what G. G. B. has mentioned about 

 water and its own level. 



It is. I believe, one of the strongest arguments uf flat 

 earthists, and the flat earth idea is certainly wrong, so there 

 must be some explanation that will answer his query. 



Is it that, taking for example a square mile of ocean, it is 



such a small area that the water certainly finds its own level 



within that radius, but taking the oceans themselves they must 



take the curvature of the earth, so in the one sense does the 



water find its own level, while in the wider sense we must also 



forget that the earth has a great power of attraction, and so 



the gravitation of the earth makes the oceans take the shape of 



the globe. . , , 



" A. Mercer. 



11. .\ BOOK ( )N W.\SPS.— In .answer to Mr. Sandeman's 

 enquiry for a book on wasps, I venture to recommend " Wild 

 Bees: Wasps and .Ynts and other Stinging Insects," by 

 Edward Saunders, F. R.S. It is a popular work of about 

 one hundred and fifty pages, with four coloured plates, and 

 other illustrations, published two years ago by Routledge. 

 The price. I think, is 3s. 6d. \f A c; 



13. THE FINDING OF THE TIME .\T XKiHT.— The 

 time may be found at night approximately by means of the 

 accompanying adjustable dial ; this may be used either by 

 direct comparison, or studied until it can be retained in the 

 memory suflftciently for comparison with observation. 



FiGlRE 1. The Dial. 



39 



