47S 



KNOWLEDGE. 



December, 1910. 



accuracy, or that we are debarred from deducing by observa- 

 tion the cardinal points, then the only alternative left, is to 

 adopt the philosophy of a modern doctrine, and .... to 

 ask a policeman. ,- ,, 



^ D. l-ERGUSSOX. 



1 J. F.R.A.S. asks how the time may easily be found by the 

 Stars, and states that Boy Scouts are required to know some 

 method before obtaining their Starman's Badge. 



The following is the method I taught the Boy Scouts here. 

 six of whom won the Starman's Badge : — 



Imagine the Polar Star to be the centre of the dial of a clock 

 (see Figure 1 ). and a line from it to y Ursae Maj. to be the hour 

 hand. On March 31st, this imaginary line from the Polar Star 

 to 7 is vertical at 12 midnight. Since all the stars rotate around 

 the Polar Star in twenty-four hours, we can at once estimate 

 approximately the tiiue by observing the 

 position of this line. Thus at 6 a.m. it 

 would be horizontal, and at 12 noon, if we 

 could then see it, it would be vertical, the 

 rotation of course taking place in a direc- 

 tion opposite to that of the hands of a 

 clock. As a solar day is about four 

 minutes longer than a sidereal day, we 

 must deduct, for any other date, four 

 minutes per day after March 31st from 

 the calculated time. 



."^n example will make this clear. Sup- 

 pose PG represents our imaginary line, P 

 being the Polar Star : on August Sth, the 

 time indicated is evidently about 9 a.m. /- 

 (PV is vertical). From March 31st to .August 

 8th is one hundred and thirty days. Hence 

 we have to deduct 520 ( = 4X130) minutes, V 



or 8 hours 40 minutes from 9 a.m., which FiGUR 



gives the time as 12.20 a.m. 



Should Ursa Maj. be obscured by clouds, many other stars 

 will do instead of y Ursae Maj. Thus, the line we have 

 supposed to be formed by joining the two stars, will pass 

 through /J Cassiopeiae. Many other combinations of stars 

 with Polaris will suggest themselves. 



(Rev.) M. Davidson, B.Sc. 



15. K.ARTH TIDES. — I should recommend for the study 

 of Earth Tides a perusal of some chapters in " The Tides," 

 by Sir G. Darwin. Then a slight grasp of the meaning of 

 tide-generating force in any mathematical text book of 

 Astronomy, and finally Dr. Hecker's own paper in the 

 Publications of the Prussian Geodetic Institute: N.F. 

 No. iZ. Berlin, 1907. The latter is in German and rather 

 inaccessible, but in the Aniiuairc ciu Bureau des Longi- 

 tudes, 1909, there is an excellent article on the subject. As I 

 see that Mr. Hodgkin is a member of the B.A.A., may I refer 

 him to the Journal, xvii, pp. 1S1-18S and pp. 233-238, also 

 xix, pp. 304-309. J. A. H. 



19. NEPTUNE'S ORBIT AND BODE'S LAW.— I do 

 not think the text-books sufficiently indicate to the student 

 how completely the computed orbits of Le V'errier and .Adams 



q pn> 



differed from the true orbit as later found by observation. 

 So great were the discrepancies that it was soon recognized 

 that it was merely the remarkable coincidence of the celebrated 

 computations having been undertaken precisely at the period 

 when the hypothetical and true orbits happened most nearly 

 to agree (namely during the twenty years or so before and 

 after the 1822 conjunction with Uranus) that had enabled the 

 discovery to be made at all upon the assumed premisses. It 

 was with no disrespect for the marvellous analyses of the two 

 great mathematicians that another eminent mathematician of 

 the time went so far as to call the discovery " a happy 

 accident." The mean distance prescribed by the empirical 

 law of Bode — to which Mr. Dixon particularly refers — was an 

 essential argument in the hypothetical orbits : under observa- 

 tion the so-called law immediately failed, and to an extent 

 computed at the time at no less than seven 

 hundred and thirty-two millions of miles. 

 Present-day figures merely add to the dis- 

 crepancy another twenty millions of miles. 

 We are not urged, then, by eitherearly or later 

 observations to regard Bode's Law — remark- 

 able as is its application to the distances of 

 the interior planets — as anything more than, 

 perhaps, another " happy accident." Put 

 finite baldly, it never did, and never will, fit 

 any observed position for Neptune. 



The remainder of Mr. Dixon's enquiry will 

 be perhaps best answered by a quotation of 

 a few of the early elements found for the 

 new planet, based on observations up to the 

 end of 1853. by which time the planet had 

 only covered in its orbit some 13 degrees of 

 arc. A comparison of these with the 

 presently accepted elements should prove 

 interesting to your enquirer. 



Elements for Neptune for 1st January 

 Mean Distance from Sun (in astronomical units) 

 Maximum ditto 

 Minimum ditto 



Eccentricity (semi-axis major=l) 

 Sidereal revolution in days 

 Longitude of perihelion 

 Inclination of orbit to ecliptic 



3prf[ 



E 1. 



1854. 



30'03627 



30'29816 



29'77438 



■0087193 



60126'722 



47° 17' 58" 



1° 46' 59"'0 



.Apparent diameter... ... ... ... ... 2"'4 



Diameter in miles ... ... ... ... ... 33610 



Volume (Earth's=l ) ... ... ... ... 76'6 



Density (Earth's = l) 0'222 



It will be seen from the comparison that, while the physical 

 values have required some revision, the orbital elements 

 found were closely correct. 



There will still remain for your enquirer's consideration the 

 very minute perturbations which have helped to the conjecture 

 (to put it no higher) of further external planetary bodies. But 

 something as to this he will have seen in Mr. Chambers' 

 " Astronomical Notes " on p. 447 of your November issue. 



W. E. Yerward-James, B.A. 



A ZOOLOGICAL GATHERING. 



On Saturday, November 12th, a most successful gathering of 

 Zoologists was held at Trinity Hall, Cambridge. The 

 festivities consisted of a dinner followed by speeches. No 

 less than eighty were present. Sir E. Ray Lankester occupying 

 the chair. The in\itation included all alumni of Oxford and 

 Cambridge who were engaged in teaching and research in 

 Zoology. The president, who was very warmly received, pro- 

 posed the toast of Zoological Science. In the course of his 

 remarks he dwelt on the necessity of bearing in mind that it was 

 the study of form that had dominated, and would continue to 

 dominate, the science to which they were all so much devoted. 

 Morphology, he said, had at least one attribute that should 

 comniend it to the authorities of the Ancient Universities, and 

 that was its absolute inutility. 1 here was, perhaps, no other 

 science that was less connected with anv form of inonev- 



making than Morphology. He congratulated himself that 

 in the whole company present there were hardh^ a dozen that 

 had not been pupils of his own, or pupils of his pupils. 

 The speeches that followed were equally worthy of the 

 occasion, especially that of the Master of Trinity Hall, who 

 was in his most humorous vein. His remarks were greeted 

 by rounds of laughter and applause. After dinner the 

 company adjourned to the quarters of their hospitable friends, 

 where informal "shop" was talked till the early hours of the 

 morning. On Sunday the zoological laboratories were opened 

 to the inspection of the more fortunate whose duties allowed 

 them to spend the week-end in Cambridge. All felt that the 

 gathering had been most successful, and much gratitude was 

 expressed to Professors Bourne and Gardiner, by whom the 

 meeting had first been thought of and organized. M. D. H, 



