QUERIES AND ANSWERS. 



Readers arc invited to scinl iii (Jiicstioiis ami to answer the Queries icliieli are printed on this paf<e. 



QUESTIONS. 



Numbers 16, 17 and IS (December number, page 4611, 

 21 (January number, page 39), 26 and 27 (February number, 

 page 49). still remain unanswered. 



28. P.\LL.A.S .\ND d .A-OU-^RII.— On September 22nd last, 

 at transit time, (a moderately good night, and Pallas being then 

 of 9-1 magnitude), the Planetoid was quite mysterionsly 

 missing to the writer in the immediate neighbourhood of 

 d .\quarii. Owing to bad weather and moonlight it had last 

 been observed only on the 13th. and was again recovered on 

 the 24th. As it had obviously closely approached d Aquarii 

 would some one of your astronomical readers care to very 

 kindly give me its position-angle and distance from the named 

 star at transit on 22nd September, or, failing that, either the 

 apparent place for the date of the star, or a 1910 mean -place ? 



I should also feel very grateful for particulars of the magni- 

 (■ude, distance and position-angle of the small companion of d. 



Asteroid. 



29. CONSTITUTION OF THE ATMOSPHERE IN 

 WINTER. — .\s deciduous trees and plants do not elaborate 

 O, nor consume CO.> during the winter, have any experiments 

 shown that there is a deficiency of O, or a preponderance of 

 COj during this season ? ,,.11 



30. FINDING THE TIME BY THE HEA\-ENLV 

 BODIES. — I have been much interested in the recent 

 correspondence on finding the time by night through obser- 

 vation of the stars. 



Might I ask whether any of your readers can go further and 

 inform me on the following problems connected with the time 

 by day ? 



(1) How can the time of the day be ascertained by 



measuring the ratio of the length of a stick to that 

 of its shadow ? As an example, imagine this ratio 

 to be one-half on May 1st, what is the time ? 



(2) .At what times in the year will the length of a stick be 



the same as that of its shadow at noon ? 



In both instances I assume the latitude of London. 



(3) Can the latitude of a place be determined by comparing 



the ratio between the length of a stick and that of its 



shadow at noon ? ,^ ^ „„„._„, 



Interested. 



31. WIRELESS TELEGRAPHY AND THE WEATHER. 

 — I have heard it stated that wireless telegraphy may be, to 

 a certain extent, responsible fur changes in weather. Can 

 any scientific reason be given for this if it be true ? 



JoHX Glas. SA^■DE^rA^•. 



REPLIES. 



10. WATER AND ITS OWN LEVEL.— Are not the 

 difficulties of G. G. B. and Mr. A. Mercer referable simply to 

 their neglect to define to themselves the meaning they attach 

 to the expression " its own level " ? The latter correspondent's 

 suggestion is that the surface of a small area of water may 

 possibly be ftat, whereas the truth is that, eliminating all 

 extraneous forces (such as centrifugal force, solar and lunar 

 attraction, winds, and — in minute wet surfaces — globular and 

 capillary attraction), no water-surface, however small, can 

 possibly be flat. In other words it can never be tangential to 

 any spherical surface, but must be itself an actual part of a 

 spherical surface, and of a curvature appropriate to its radial 

 distance from the Earth's centre. Conseciuently, that which 

 the surface of any body of water — if disturbed — does again 



seek is "' its appropriate spherical curvature " ; and if the word 

 '' level " be assumed necessarily to mean a plane surface then 

 the whole expression " Water finds its own level " must be 

 considered not only unscientific but directly untrue. 



If the above statement of theory be accepted the following 

 occur to me as some of the more curious of the necessary 

 results : — 



If the rotation and revolution of the Earth were suddenly 

 stopped (again we must eliminate external gravitational forces, 

 as also the moment of inertia), the equatorial oceans would 

 immediately flow away northwards and southwards, in an 

 attempt to reduce the spheroidal wet surface of our globe to 

 that of a true sphere. 



.Again, under existing circumstances, the surface of the 

 Dead Sea is no less than one thousand two hundred and 

 ninety-two feet below that of the neighbouring Mediterranean. 

 Consequently, being part of a sphere of lesser radius, any 

 circular acre (say) of the former sea will have a wholly 

 difterent surface-curvature from that of a circular acre of the 

 Mediterranean, and — sequentially — a lesser right horizontal 

 diameter. 



Much more markedly will a given area of ocean in equatorial 

 regions differ from the same in polar regions. 



More strikingly still follows this fact, that any particular 

 portion of the ocean-surface must have different curvatures, 

 even at high-water and low-water respecti\ely ; and 

 consequently that the tables for calculating horizon-dip and 

 distance given in such books as "'Chambers' Tables" and 

 " Molesworth's Formulae " can only be averages or approxi- 

 mations, since they can only strictl\- be true for one latitude 

 or one state of the tide. 



Lastly, one has, of course, to admit that the surface of a 

 stationary cup of tea varies momentarily, owing to the lunar 

 and solar tides caused in it. But what seems to me to require, 

 perhaps, even a larger degree of imagination, is to realize that 

 the surface of the liquid must undergo a continuous alteration 

 of curvature even as one raises the cup from the table to 



lips. 



W. E. Yerward- James. 



13. THE FINDING OF THE TIME AT NIGHT.— To 

 find the time at night without instruments or notes of any kind, 

 it is necessary to acquire the faculty of estimating, by eye, the 

 distance in time of any star from the meridian. 



The imaginary arc representing the latter can be readily 

 conceived by reference to the Pole Star. Having determined 

 the first-named element the remainder is a simple question of 

 Right .Ascensions (R..A.). 



Commit to memory R.A. of a very few conspicuous stars 

 and learn to recognise them at sight. 



The R.A. of the Sun is still easier, it being only necessary to 

 recollect that it starts from O'' O" at the vernal equinox, 

 March 22ud. and increases two hours per month till the annual 

 round is complete at twenty-foiu' hours. 



Proceed as follows : — 



R..A. of star + or — time from meridian = R..A. of Latter. 



R.A. of meridian 4- or — R.A. of Sun = time. 



Example, January 5th, 1911. 



Sirius in S.E. quarter, apparently 3'' 30"' E. of meridian. 



R..A. of Sirius ... 

 Deduct ... 



40" 

 3" 30" 



R..-\. of meridian 3'' 

 R.A. of Sun deduct 



10"'+ 24" 



19" 



10" 

 0" 



Time = S" 10'" p.m. 



Edmun'd Rourke. R.K. 



103 



