Dec. 7, 1883.] 



♦ KNOWLEDGE ♦ 



361 



dark limb at 81i. 14m. p.m., at a vertical angle of 230°. Finally, on 

 the night of the 18th, 16 Sextantis, a star of the 6th magnitude, 

 will disap2)oar at the bright limb of the moon, at an angle of 45" 

 from her vertex, at llh. 6m. It will subsequently reappear at 

 8 minutes after midnight from behind her dark limb at an angle from 

 her vertex of 204°. At noon to-day the moon crosses the boundary 

 between Aquarius and Pisces, which last-named constellation she 

 does not quit until the same hour on the 10th. She then passes 

 into Aries, her passage across which occupies until 3 a.m. on the 

 12th, when she enters Taurus. She remains in Taurus until 10 a.m. 

 on the 14th, at which time she moves into the extreme northern 

 part of Orion ; this takes her 11 hours to traverse, and she leaves 

 it for Gemini at 9 o'clock the same evening. She occupies imtil 

 11 a.m. on the 16th in crossing Gemini, which she then leaves for 

 Cancer. At 2 a.m. on the 18th, she crosses the boundary into Leo, 

 and at 9 p.m. on the same day descends into Sextans, which she 

 takes just 24 hours to traverse, returning to Leo at nine o'clock at 

 night on the 18th. She quits Leo for Virgo at 11 p.m. on the 20th, 

 and is still in Virgo when our notes terminate. 



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IS THE SUN GREEN? 



[1034] — The double stars present the phenomenon of suns with 

 complementary lights. All stars do not appear to shine with white 

 light. May it not, then, be possible that our sun appears green to 

 the eyes of beings in other solar systems than ours ? " But if it 

 were green, it would be seen to bo green," most persons would 

 exclaim. This, however, is by no means a necessary consequence. 

 My contention is, on the contrary, that the eye becomes insensitive 

 to the tone of the light bij which it is illuminated ; as young artists 

 find to their cost in first attempting to paint by artificial light. 

 Unconscious of the yellowness of their j/os-sun, they take no 

 account of the altered values of their yellow pigments. Objects 

 reflecting vibrations of the same periodicity as the gas-light 

 will appear white j and so it would bo if the artificial source 

 of illumination were of any other hue, say, for instance green ; 

 in which case, the green tints of the same periodicity as the 

 illuminating source would also appear white,* and so on. This 

 may be illustrated by various experiments. Moreover, I am induced 

 to believe that our sun appears green in jilanetary systems lighted 

 by stars shining with other coloured lights than our own, from the 

 fact that green occupies the mean position in the prismatic spec- 

 trum, and therefore represents the average effect which is produced 

 oil eyes outside of our solar system, by the neutralising action of 

 the rays, of opposite periodicities, on each otiier. The values of 

 the mean elements of any two correspondingly opposite colours, 

 both in Young's and in Ilerschel's tables of wave lengths, Ac, too 

 closely agree in every case, with the numerical values of the central 

 green, to be regarded as a fortuitous coincidence. 



In the foregoing remarks I have used the language usually 

 adopted in writing and speaking on the subject of light, although 

 it is very incorrect and very misleading, but it is difficult to do 

 otlierwise, without resorting to considerable circumlocution. Never- 

 theless, according to the undulatory theory — and strictly scientifi- 

 cally speaking — objects, the sun included, only appear to be either 



* Whiteness is, in my view, the effect of the neati*alised, or 

 average, action upon the retina of any special series of vibrations. 



luminous or of certain colours. These phenomena of light and 

 colour are really but the affections of sense, appearances produced 

 in us by mechanical vibrations of various wave lengths, &c. They 

 do not "inhere, as most people suppose, in the vibrations and the 

 objects themselves. An expedition undertaken in order to discover 

 whether the sun be red, green, or violet would, therefore, if the 

 words were literallv interpreted, be simply an absurdity. 



W. Cate Thomas. 



STRANGE COINCIDENCES.— DOUBLING OF CAPITAL, &c. 



[1035]— In reference to the motion of the magnetic poles, Sir 

 Snow Harris makes the following observations : — " By a curious 

 coincidence these periods (1740, 860, 4609, 1304 years) involve a 

 number, 432, sacred with the Indians, Babylonians, Greeks, and 

 Egyptians, as being dependent on great combinations of natural 

 events. Thus, the periods 860, 1304, 1740, 4609, become, by a 

 slight modification, 864, 1,296, 1,728, 4,320, which are not inad- 

 missible, considering the complicated nature of the observations 

 from which the first numbers are derived. Now, these numbers 

 are each equal to 432 multiplied by 2, 3, 4, and 10 successively. 

 According to the Brahmin mythology, the world is divided into 

 four periods, the first being 432,000 years, the second 432000 x 2, 

 the third 432000 x 3, the fourth 432000 x 10. It is also, according 

 to Hanstein, not unworthy of remark that the sun's mean distance 

 from the earth is 432 half radii of the sun ; the moon's mean 

 distance 432 half radii of the moon ; but what is more especially 

 striking is the cu-cumstance " that the number 250920 = 432x60 

 is the smallest number, divisible at once by all the four periods, and 

 hence the shortest time in which the four poles can accomplish a 

 cycle. Now, this time coincides exactly with the period in which 

 the precessions of the equinoxes complete their circle — certainly a 

 curious and remarkable series of coincidences." 



Problems concerning the doubling of population, capital, &c., may 

 be solved by the following formula, which is, I think, simpler than 

 that furnished by your correspondent " T. J. B." (972) : — 



(l + -\"'=-- Here x or n may be readUy found. The reason 

 for the rule is also very plain; thus: Let a = the number of 

 people or amount of capital and - the first year's Increment ; then 



a + -= number at end of first year. 



(1 + - + = a -H 2- -t- - = number at end of second year. 



number at end of 

 third year. 



L X x'J X \ X X- x^/ 



Or generally a + m--t n--i- p-^,+ &c., m, n, p, &c., being the co- 

 efficients of the binominal (l-f-)" = number at end of nth 



/ 1\„ „ (. \Y^o 



year. We can therefore put n ^1 -I- - J = 2.a; ov y. + ^f 



1 

 Whence 1-1--= lyi 



i=V2-l 



Ex.— At what rate must a population increase annually in order 

 to double itself in 100 years ? 



(,,iy.=,„H.- 



In what number of years will a population, increasing at this rate, 

 double itself y 



(l-f-00605)" = 2 



Log 2 



30103 



Log 100695 -00300 



