(12526) C. H. K. asks: 1. It is held I think by most astronomers that the pole of the heavpns traces a complete circle around the pole of the ecliptic in about 25,000· years, and has for its center the pole of the ecliptic. There is also a decrease in the obliquity of the ecliptic of about 45 seconds in a cpntury. Now, how can the pole of the ecliptic be the center of the circle traced by the polL of the heavens when the distance is gradually decl'easing between them? As the obliquity of the ecliptic is equal to the radius of this circle, we would then have a circle in which the radius is constantly changing, which is I think quite impossible. A. In an exact sense it is true that a curvc with a radius which varies cannot be a circle, as you say; but since the obliquity of the ecliptic changes by only a few seconds in 100 years. while the prec(ssion of the equinox"s is about 50' seconds in one year, the changp in the radius of the pr(ces-sional effect on the pole of the hpavens is almost infinitesimal in one year. We think astronomers are quite warranted in speaking of the motion of the pole of the heavens as in a circle around the pole of the ecliptic, although sOlme usc the better term “cycle,” since the variation in the obliquity of the ecliptic is also in a cycle. At some remote time it will return to its present value. 2. What was the obliquity of the ecliptic in 1900: A. The obliquity of the ecliptic for 1900 waoS 2a deg. 27 min. 8.02 sec, as given in Todd's “New Astronomy,” page 150, a book which we send for $1.50. :. Is there any evidence to show that an individual organism has the power to modify its,lf physically to meet a change in environment, or meet conditIons to which it is not adapted '! A. Probably an individual organism has not the power to modify itself radically to meet a sudden change of environment to which it is not adapted. 4. Is there anything to show that evolution takes place apart from natural selection'! A. All the causes of change in species and indiv,;duals, and not natural selection alone, are involved in the proof of the theory of evolution. The literature of the subject is very pxtCnHive, beginning from Darwin's “Origin of Species,” which we will send for $2. Many articles have from time to time been printed in our Supplement, (12527) R. A. S. asks: What is the astronomical name of the star which is known as the star of Bethlehem, which guided the shepherds and the wise men at the birth of Jesus Christ and can be seen in Palestine every year on and about December 25th? A. There is no star known to astronomers as the “Star of Bethlehem.” 2. Would a postage stamp vending machine pay'! In the large post offices a great deal of time and bother is taken in handling and sellmg postage stamps. “ould It not pay the Government to have machines in the large cities eliminating this trouble? A. There are several kinds of stamp vending machines in use in many CItIes, both 1 Amelca and Europe. We do not know whether they are profitable 01 n ot . 3. What are the advantages of raising the “Maine"? Does it not cost more to raIse It than the old hull is worth'! A. The raising of the “!faine” clears a dangerous obstruction from a friendly harbor, enubles us to give burial to the bodies of the men who died in the service M their country on this ship, and may clear up the tmcertainty as to the cause of the exVlosion. Any one of these reasons is quite sufficient to justify the expense of the work. The old hull is worthless. It was long ago corroded by salt water, and was SiD twisted by the explosion that it conld not be rebuilt to b( of any value. Its only pecuniary value would be as old metal. (12528) J. C. 0_ says: Regarding a differential gear on an automobile using say 40 horse-power, A claims that in traveling in a straight line the same amount of power is applied to both drive wheels, but that in turning a corner the power is shifted to the outside drive wheel, and that if it were required practically the full (40) horse-power would be exerted on this outside driver. B claims that in making the twrn as much power is exerted on the inside driver as on the outside ; in other words (if it were required) 20 horse-power on each driver. Which is correct· A. The driving gear of automobiles is designed to exert an equal turning movement on each driven wheel at all times. If an automobile could be steered so sharply to one side that one rear wheel stood still while the other turned aronnd it in a circle (this might be done by a three-wheeled car) the stationary wheel would be pulled on by the gearing just as hard as the moving wheel: but as it could not turn no “work” would be done upon it, and the “work” of turning the car would be .done by the moving wheel entirely. Do not confound jorce with work . ill Iatte'!' implies motion in the direction of the force which produces it.